Integral Waterproof Concrete A Comprehensive Review
Integral Waterproof Concrete A Comprehensive Review
Integral Waterproof Concrete A Comprehensive Review
A R T I C L E I N F O A B S T R A C T
Keywords: The ingress of water and aggressive substances is the primary reason for the chemical and
Waterproof concrete physical degradation of concrete infrastructure, leading to a reduction in durability and
Hydrophobic concrete a shortening of life span. In practice, different integral waterproofing admiXtures and
Waterproofing admiXtures surface coatings have been widely used to prevent or mitigate this problem. Compared with
Mechanical properties surface protection, the incorporation of integral waterproofing admiXtures (such as densifiers,
Durability
water repellents, and crystalline admiXtures) in concrete has several benefits, such as ease of
Sustainability
applica- tion, elimination of regular maintenance, and little or no deterioration over time. So far,
there is no comprehensive review on integral waterproofing admiXtures and their effects on
various properties of concrete. This review examines existing literature on integral waterproof
concrete containing various commercial and laboratory-made waterproofing admiXtures. This
compre- hensive review highlights that the use of integral waterproofing admiXtures has the
potential to increase the service life and improve the durability of concrete structures and
infrastructure. However, the admiXtures may have a negative impact on some concrete
properties, such as workability and strength. Whilst many hydrophobic and crystalline
admiXtures can reduce the water absorption rate of concrete by up to 80%, they often have a
negative impact on the concrete compressive strength, causing a strength reduction of about
10% or more. Their influence on some durability properties (e.g., reinforcement corrosion,
microbial-induced concrete corrosion) is inconclusive, indicating the need for further research.
There is also a need to develop proper guidelines to determine the efficacy of integral
waterproofing admiXtures. More research is also required to assess the long-term performance
of integral waterproof concrete and its benefits based on life cycle assessment.
1. Introduction
Concrete is inherently porous and has numerous microcracks in the matriX, making it vulnerable to the ingress of water and
other aggressive fluids. A reduced life span over time is expected for concrete infrastructure exposed to an aggressive environment
because of physical and chemical degradation [1]. Likewise, concrete infrastructure located near the groundwater table or in a
highly humid environment is also susceptible to deterioration due to the ingress of water [2]. Without intervention,
significant maintenance for critical infrastructure is required with high associated repair costs. To reduce/eliminate the need for
maintenance, suitable measures can be adopted to significantly reduce the water absorption rate of concrete [3–5].
Currently, there is no universally accepted definition for waterproof concrete (also known as water-resistant and
watertight
* Corresponding author.
E-mail address: z.tao@westernsydney.edu.au (Z. Tao).
https://doi.org/10.1016/j.jobe.2023.107718
Received 14 June 2023; Received in revised form 31 July 2023; Accepted 2 September 2023
Available online 9 September 2023
2352-7102/© 2023 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY license (
http://creativecommons.org/licenses/by/4.0/).
S. Jahandari et al. Journal of Building Engineering 78 (2023) 107718
concrete). The German Committee on Reinforced Concrete [6] defines waterproof concrete as that with a water absorption rate
reduced by more than 50% in comparison to untreated reference concrete. According to the National Corporation of Highway
Research Program in the USA [7], the water absorption rate of waterproof concrete should be less than 2.5%. In the British Standard [
8], it is stated that waterproof concrete should have the ability to prevent moisture movement from one place to another. Despite the
different definitions, it is clear that waterproof concrete should have a relatively low water absorption rate.
Various measures have been adopted to reduce the water absorption of concrete. Traditional methods include adding
supple- mentary cementitious materials (SCMs) to the concrete miXture, reducing the water-to-cement (w/c) ratio, and using
additional reinforcement to control concrete cracking. More recently, researchers proposed a few other methods for developing
waterproof concrete, such as the use of external membranes, surface coatings, or integral waterproofing [1,9]. In particular, the
use of integral waterproofing admiXtures has been considered a viable alternative to the other commonly used waterproofing
methods [1]. In this regard, many different integral waterproofing admiXtures have been tried, and the findings show that their
effectiveness in reducing water absorption varies significantly [10].
The use of integral waterproofing admiXtures aims to turn the concrete itself into a water barrier. In contrast, external membranes
or surface coatings only form a barrier on the top or bottom surface of the concrete. Therefore, integral waterproof concrete does
not require regular maintenance and can be used in structures, such as deep foundations and tunnelling works, where it is challenging
to apply a layer of protection [11]. Furthermore, the effectiveness of coatings and waterproof membranes is susceptible to surface
damage or concrete cracking during the service life [1]. Once damaged, the water absorption rate and permeability of the concrete
increase dramatically [12,13]. However, the permeability of integral waterproof concrete will not be affected by any surface worn out.
Thus, integral waterproof concrete could potentially have improved durability performance than concrete with a surface protection
layer [1]. But additional measures should be adopted to prevent water ingress at concrete joints or locations with the potential to
develop large cracks.
Integral waterproofing admiXtures in liquid or powder form can be incorporated into concrete in batching plants. Such
admiXtures can be classified into three categories: densifiers, water repellents (also known as hydrophobers), and crystalline
admiXtures. Den- sifiers refine the pore size distribution of concrete and densify the cement matriX, whereas water repellent
admiXtures change the surface tension within cracks and pores to raise the liquid contact angle, thereby resisting absorption [14,15
]. In contrast, crystalline admiXtures are reported to increase concrete resistance against water penetration under pressure by pore
blocking arising from solids deposition through chemical reactions [16]. The most widely used densifiers are various SCMs, such as
silica fume, fly ash, and slag. The efficacy of these densifiers in decreasing concrete water absorption has been well established, but
they can seldom reduce water absorption by over 30%. Thus, the developed concrete by only adding SCMs cannot be
recognised as waterproof concrete [17]. Therefore, this review will mainly focus on concrete with hydrophobic and crystalline
admiXtures. Typical hydrophobic admiXtures include silicone-based compounds, fatty acids, calcium stearate, and fats and oils.
Recently, crystalline chemicals (e.g. sodium acetate) have also been used in concrete due to their capability to enhance the
concrete’s self-sealing properties [16].
Table 1 summarises recent review articles [3,4,18–21] published on waterproof concrete to demonstrate the need for the present
review paper. As can be seen in this table, most of the previous review articles are focused on surface coating technology and its effects
on the mechanical properties and long-term durability of concrete. There is no comprehensive review on the effects of various integral
waterproofing admiXtures on concrete behaviour. Accordingly, the objectives of this paper are threefold. First, the mechanisms and
limitations of various integral waterproofing admiXtures will be reviewed based on the current state of knowledge of the interaction
between the integral waterproofing admiXtures and concrete. Second, the effects of integral waterproofing admiXtures on the
con- crete’s fresh, mechanical and durability properties will be critically analysed. Finally, crucial insights and recommendations for
further
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2. Research significance
Substantial research has been conducted over the past decades on the development and application of different
waterproofing admiXtures and surface coatings/membranes for concrete protection. There are a few existing review articles in this
area that sum- marise the research outcomes of surface coatings/membranes. However, to the best of the authors’ knowledge,
there is no review paper on integral concrete waterproofing admiXtures and their effects on various properties of concrete. It
is necessary to review various waterproofing admiXtures and chemicals based on the mechanisms of developing water resistance.
The present study addresses this gap. Accordingly, the waterproofing admiXtures are categorised based on their waterproofing
mechanisms, and the influence of these admiXtures on the fresh, mechanical, and durability properties of different types of concrete
is discussed. Requirements for future research as well as the challenges and limitations of using waterproofing admiXtures in
concrete are also presented. This review will expand the prospects of researchers and engineers who are closely associated with
the concrete waterproofing industry. Compre- hensive data were used to assess the impact of various types of integral
waterproofing admiXtures on the concrete properties.
3
Table 2
al.
S. Jahandari et
Mechanisms and features of different types of integral waterproofing admiXtures.
Densifiers React with the calcium hydroXide produced in hydration and create by- • Not characterised as waterproofing or hydrophobic Slag, fly ash, metakaolin, rice husk ash, silica fume, nano-
product materials, slowing water migration and increasing concrete materials since they cannot seal joints and cracks. SiO 2 , nano-Al2 O 3 , nano-Fe2 O 3 , and fluorosilicate-based
density • Under hydrostatic pressure, it requires additional admiXtures [14,15,22]
waterproofing treatment to preserve concrete from
degradation and damage.
• Concrete overall cost can be reduced by using appropriate
proportions in the miX design.
• Can be used as a partial replacement of Portland cement.
Water-repellents Silicone-based Waterproofing admiXtures develop polymer barriers • Usually used in massive concrete structures, including Everdure Caltite, Conqor B52, and Hycrete are some of the
compounds inside pores during the hydration process. commercially available water-repellent admiXtures.
These admiXtures typically exist in liquid form and • Can be found in the form of liquid emulsions or as powder
include long-chain fatty acids (LCFA) derivatives, additives [23].
stearates, oils, and hydrocarbons. • Prevent concrete from breathing due to the alkoXy group
Performance of these compounds is highly reliant on that forms its molecular structure [24].
the concrete itself. • These products have a detrimental impact on the
environment and natural resources as their main
component is made from organic materials [25].
• EXpensive and poor wear resistance [26,27].
Fatty acids Neutralised fatty acid salts are used as hydrophobic • Sometimes these types of admiXtures produce a wax-like Solid fatty acid, especially stearic acid, is extensively utilised
admiXtures. compound that coats the capillaries surface during the as a hydrophobic admiXture. Liquid fatty acids,
including evaporation process, which results in hydrophobic caprylic, oleic, and capric acids, can also be used as
behaviour. hydrophobic admiXtures.
• A contact angle of 180◦ has been achieved with this
method [28].
4
Metallic One of the basic properties of metallic stearates is water • Reduced permeability and bulk and capillary water Calcium stearate, aluminium stearate, and zinc
stearates repellency. stearate
absorption have been reported for concrete incorporated
metallic stearate under non-hydrostatic conditions [29].
Fats and Vegetable oils can be applied as a hydrophobic • A relatively small quantity (0.5-1.5% of cement weight) is Rapeseed, peanut, silicone and olive oils.
oils admiXture for concrete and mortar if an appropriate needed.
distribution is obtained by dispersing the oil in water • Oils with a high amount of monounsaturated fatty acids
before blending. appear to be the most influential.
• Rapeseeds oil seems to be the most attractive option from
a concrete technology perspective, mainly as it can be
produced in cold climates [30].
Wax and Finely divided wax emulsions are influential • A reduction in compressive strength of 4% could be Waxes with a melting point range of 57-60 ◦ C are used with
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Journal of Building Engineering 78 (2023)
polymer hydrophobic admiXtures. Emulsions break down after observed when added at the proportion of 3% to the an emulsifying agent based on ethoXylated sorbitan
emulsions contact with alkaline water in concrete pores and form binder (cement) [31]. monostearate or sorbitan monostearate.
a hydrophobic layer.
Crystalline Unlike hydrophobic counterparts, crystalline admiXtures use available • These admiXtures are hydrophilic in nature and exist in a Sodium acetate [32,33].
admiXtures water to grow crystals inside the concrete – efficiently sealing off the dry, powdered form.
moisture pathways. • Crystalline technologies have self-sealing ability.
• Crystals within the concrete are invulnerable to physical
deterioration and damage; there is no danger of tears,
punctures, or seam leaks.
S. Jahandari et al. Journal of Building Engineering 78 (2023) 107718
3.1. Densifiers
Most densifiers can react with calcium hydroXide [Ca(OH)2] generated in cement hydration, creating another product that
in- creases concrete density and slows water migration. Since densifiers are less effective than water repellents and crystalline
admiXtures in reducing water absorption, some researchers do not consider densifiers as waterproofing admiXtures [10,15].
Nonetheless, den- sifiers can still slow water migration in concrete matriX and are often used in combination with water
repellents or crystalline ad- miXtures to develop waterproof concrete.
The most widely used densifiers in concrete are SCMs and some nanomaterials (e.g., nano-SiO 2, nano-Al2O 3, and nano-Fe2O 3). The
effects of these materials on the fresh, mechanical and durability properties of concrete have been well studied [14,34]. It is generally
believed that pozzolanic reactions of SCMs change the microstructure of concrete and the chemistry of the hydration
products by consuming the released calcium hydroXide and producing additional calcium silicate hydrates (C–S–H). This leads
to increased strength and reduced porosity and therefore improved durability [35]. It has been reported that a more uniform
and compacted microstructure was created after incorporating nano-SiO2 in normal concrete (see Fig. 3) [36]. As nano-SiO 2 has very
high activity due to its galactic specific surface area, it can react with Ca(OH)2 crystal quickly to produce C–S–H gel, which fills the
voids to enhance the density of the interfacial transition zone (ITZ) and the binding paste matriX. As can be seen in Fig. 3b, a large
amount of C-S-H gel has been formed in concrete containing nano-SiO2, which cannot be seen in the reference paste without nano-
SiO2. Therefore, the stability and integration of the hydration product structure are enhanced, leading to improved durability and
long-term mechanical properties of concrete. Other types of nano particles, such as Fe2O 3 and Al2O 3, also have similar filler effects
and/or pozzolanic activity on the
Fig. 3. Microstructure of normal concrete incorporating fly ash: (a) without nano-SiO 2 ; and b) with nano-SiO 2 [36].
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Fig. 5. Coupling mechanism of mica and PDMS using a silane coupling agent [39].
Fig. 6. Surface morphology: (a-c) untreated concrete; and (d-f) treated concrete [43].
Fig. 7. Concept of turning waste newspaper into an admiXture for producing hydrophobic concrete [9].
cementitious matriX [34]. It should be noted that concrete with densifiers normally has limited self-healing capacity. Thus,
such concrete may not be suitable for sealing joints or cracks.
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Fig. 8. Hydrophobic GGBS powders: (a) effects of stearic acid content and milling time; and (b) effect of milling speed [26].
used in combination with other admiXtures. Therefore, these admiXtures are most suitable for non-critical areas with low water
tables or above-ground applications. Different types of water repellents are summarised in Table 2 and reviewed as follows.
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2. Fatty acids
Diluted or undiluted liquid fatty acids, including caprylic, oleic, and capric acids, can be used as hydrophobic admiXtures
in a concrete miX. In particular, solid fatty acid, i.e., stearic acid, has been extensively utilised as a hydrophobic admiXture
and can be added directly to concrete in powder form [43]. Fig. 6 shows the scanning electron microscopy (SEM) images of concrete
treated with and without stearic acid. As can be seen, the pore size of the untreated concrete is larger than that of the treated
concrete. The treated concrete had a rough and convex structure, as shown in Fig. 6d and (e). The rough structure consisted of
acicular ettringite and fine calcium stearate, as can be observed in Fig. 6f. Under the influence of stearic acid, the hydrated
product is superimposed with a needle-like structure that can make the concrete rough to create the Cassie-Baxter state, which is
essential for the concrete to maintain superhydrophobicity [43]. Stearic acid can also be premiXed with inert fillers, like silica
or talc or an emulsion in water to help dispersion throughout the miX [31]. Furthermore, it can also be used as a modifying agent
to produce hydrophobic waste-based sand to substitute natural sand in mortar or concrete [44,45]. Song et al. [44] recently used 7%
stearic acid as a modifying agent to prepare superhydrophobic oyster shell powder. Mortar with 30% replacement of the
superhydrophobic oyster shell powder showed a water contact angle of 95.2◦ . In another study [45], 1.5% stearic acid was reported
to be the optimum amount to modify iron ore tailings, and 30% hydrophobic iron ore tailings powder was added to mortar to
achieve the hydrophobic state. However, although such water repellent agents are considered economical, they often have a
negative impact on the mechanical properties of concrete, limiting their wide application in practice.
Pre-treated hydrophobic admiXtures can also be made with fatty acids and used to improve the water repellent property of
con-
crete. Hydrophobic paper sludge ash (PSA) and ground granulated blast furnace slag (GGBS) powders have been converted into
hy- drophobic powders by milling with stearic acid to functionalise the powders [9,26]. The concept of turning waste newspaper
into a hydrophobic admiXture and then developing hydrophobic concrete is indicated in Fig. 7. It was reported that the dry ball
milling speed and time had substantial impacts on the hydrophobic performance of such hydrophobic powders, as shown in
Fig. 8. Therefore, optimisation is required to find out the optimal milling speed and time and the type and ratio of raw
ingredients. Thus, the quality control of the hydrophobic admiXtures in mass production could be challenging. In recent research
conducted by the authors [10], different hydrophobic powders (e.g., GGBS, fly ash, and glass) treated with 2% stearic acid were
prepared and used to develop hy- drophobic concrete. Although the water absorption rate of the treated concrete could be reduced
by up to 30%, it was still too high to meet the water absorption limits specified for waterproof concrete in Refs. [6,7]. Shi et al.
[46] also developed a hydrophobically modified steel slag using stearic acid via chemical treatment, and the slag with 1% stearic
acid improved the water contact angle of the treated mortar up to 91.5◦ .
3. Metallic stearates
Stearates, such as calcium stearate, aluminium stearate, and zinc stearate, are derived from fatty acids and are readily available
for
use in concrete. They can provide a hydrophobic coating to capillary pores and consequently restrict water transfer in concrete
under non-hydrostatic conditions [47]. According to the authors’ recent research [10], calcium stearate might be a promising
material for developing integral waterproof concrete. It reacts with water and cement to produce a hydrophobic wax-like product,
which coats the surfaces of capillaries after water evaporation. Besides, calcium stearate often has a particle size ranging from
nanometres to a few microns, which can also seal micropores in concrete [47]. Most stearates, such as calcium stearates, have a
negative impact on the workability and mechanical properties of concrete. Nonetheless, these negative effects could be mitigated by
adding other admiXtures, such as superplasticisers and SCMs.
Fig. 9. Crystalline waterproofing admiXture in concrete: (a) voids; (b) crystal growth in voids; and (c) sealed voids [
50].
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Fig. 10. Self-healing of shrinkage cracks: (a) formation of shrinkage cracks; and (b) cracks healed by nanocrystals [51].
Crystaline admixtures can reduce the rate of water loss in fresh concrete,
resulting in less shrinkage.
Fig. 12. Bonding and interaction between concrete and sodium acetate [52].
based systems typically exist in a dry powdered form and are hydrophilic in nature, which means they absorb water. Unlike
their hydrophobic counterparts, crystalline systems use available water to grow crystals inside the concrete, closing off
pathways for moisture to seep into the concrete. In contrast to water repellents, crystalline technologies are reported to enable self-
sealing after a crack is generated, as penetrated water can trigger new crystal growth to seal the crack [33]. Therefore, the concrete
with self-sealing ability becomes a water barrier again, as shown in Fig. 9 [50]. When the moisture content in concrete is low, voids
can be clearly seen in the concrete (Fig. 9a). After absorbing water, crystals start to grow in the voids, as can be seen in Fig. 9b. After a
certain period, the voids are mostly sealed by formed crystals, as shown in Fig. 9c. It has been reported that crystalline formulas can
seal hairline cracks with a width up to 0.51 mm [51], which can be seen in Fig. 10. Fig. 11 summarised the potential benefits of
crystalline admiXtures over other waterproofing admiXtures. However, a few researchers have reported that some commercial
crystalline admiXtures reduced the mechanical strength of concrete, which will be further discussed in Section 4.
As a typical crystalline admiXture, sodium acetate has been recommended to extend the service life of concrete and improve
its
durability without affecting its strength [32,52]. Fig. 12 shows the interaction between concrete and sodium acetate to form
water- proof concrete. However, according to the authors’ research [10] and results reported by others [42,53], the water absorption
rate of concrete with sodium acetate is greatly affected by its w/c ratio. Hence, to develop waterproof concrete in practice by using
sodium acetate, trial tests should be conducted to choose a suitable amount of sodium acetate for concrete with a specific w/c ratio.
Otherwise, sodium acetate may even negatively increase the water absorption of concrete if the amount of sodium acetate is not
optimal. Besides, sodium acetate takes time to form crystals. Therefore, it may not be effective for early-age concrete.
Moreover, according to un- published research conducted by the authors, sodium acetate is more effective in reducing the water
absorption rate of concrete when it is dissolved in the miXing water than used in powder form to miX with other solid ingredients.
Dissolving in water might improve the dispersion of sodium acetate in the concrete miXture.
Based on the above discussion, the following points can be drawn:
• Densifiers should be used in simple structures as they cannot seal joints and cracks. These admiXtures can be used as a
partial replacement for Portland cement.
• Water-repellent admiXtures can effectively increase the water contact angle, but they often decrease the mechanical strength
of concrete.
• Using crystalline chemicals, such as sodium acetate, might be an effective method of improving concrete’s waterproofing
properties to some extent if properly used. They are reported to heal new concrete cracks in the service stage as well.
• Several studies suggested the use of hybrid admiXtures, such as the combination of water-repellent and crystallising
admiXtures. However, extensive studies should be conducted to evaluate the financial and technical feasibility.
Among different waterproofing admiXtures, silane/siloXane-based products, stearates, and crystalline admiXtures are
getting popular among concrete practitioners. Nonetheless, the selection of a waterproofing admiXture should consider the service
conditions and required performance of the structure. Meanwhile, the influence of the waterproofing admiXture on the fresh,
mechanical and durability properties of the concrete should also be considered. For example, when a structure is exposed to a small
or no hydrostatic pressure, densifiers and/or water repellents are often sufficient to reduce water penetration. However,
hydrophilic crystalline chemicals such as sodium acetate might be more suitable for structures under hydrostatic conditions if
properly used [24].
yield stress and plastic viscosity values, whilst the thiXotropic behaviour was slightly reduced. Slump flow and V funnel tests
conducted on the SCC showed that the hydrophobic admiXture had a negligible influence on the slump flow but slightly increased
the viscosity. Madduru et al. [60] used liquid paraffin wax as a hydrophobic admiXture. When a dosage of 1% by weight of cement
was added to SCC, its slump flow decreased from 780 mm to 735 mm, and the V-funnel flow time increased from 9.98 s to
10.55 s. Nonetheless, the influence of adding the hydrophobic admiXture was not significant, and the fresh properties of the
modified SCC still met the re- quirements of European guidelines for SCC. Tian and Qiu [61] studied the effect of a silane-based
solution with a solid content of 40% on the flowability of self-compacting rubberised concrete. It is worth noting that the dosage of
the hydrophobic admiXture added to the SCC was relatively high (2–6% by the weight of cementitious materials or 11.7-35.2
kg/m3). It was found that increasing the hy- drophobic admiXture dosage slightly increased the viscosity and segregation
resistance of the fresh concrete miXtures. However, in contrast with the findings reported by Madduru et al. [60], Tian and Qiu [61]
found that the hydrophobic admiXture slightly increased the flowability, filling ability, and passing ability of the SCC. For
example, adding 4% hydrophobic admiXture to the SCC without rubber increased its slump flow from 740 mm to 780 mm. Tian
and Qiu [61] attributed this increase to the adsorption of hydroXyl groups from the hydrolysis of the silane/siloXane molecules on
the surface of the cement particles, which reduced agglomeration and freed up the water that was previously confined by the
agglomerated particles. In general, it seems that the influence of hydrophobic admiXtures on the fluidity of SCC is not significant.
Only limited studies have been conducted on the effect of integral waterproofing admiXtures on the setting time of concrete.
Most waterproofing admiXtures were found to shorten the setting time of concrete. It has been reported that calcium stearate
reduced both the initial and final setting times of reinforced concrete, and the rate of acceleration decreased with increasing calcium
stearate [47]. Spaeth [62] also reported shortened setting time of concrete treated with siloXane and silane. However, mortar samples
containing two commercial waterproofing admiXtures (Conplast X421Ic and Conplast WP90) were reported to have prolonged initial
and final setting times than the reference samples [63]. Meanwhile, the use of excessive amounts of hydrophobic admiXtures may
also result in pro- longed setting time [64]. Therefore, trial tests would be advisable to check the setting time of concrete
with an overdosed water- proofing admiXture [65].
The impact of waterproofing admiXtures on the concrete workability (i.e., slump) is important for choosing a suitable
water- proofing admiXture in field applications. For a specific application, a minimum slump value is often specified considering the
distance between the reinforcement and ease of vibration, etc. When a waterproofing admiXture significantly reduces the concrete
workability, a higher amount of water or superplasticiser has to be added to achieve the target slump. Thus, it might adversely affect
the concrete strength and shorten the durability and service life of the concrete. Therefore, caution must be exercised when
using such water- proofing admiXtures in real applications. It should also be noted that a waterproofing admiXture might
react with other concrete admiXtures (e.g., superplasticiser) and jeopardise the properties of concrete. If there is no prior
knowledge, trial tests are recommended to ensure that the designed concrete miX with a waterproofing admiXture has suitable
workability and setting time for field applications.
Pre-treated hydrophobic admiXtures usually have pozzolanic activity. By using up to 8% hydrophobic PSA, no significant adverse
impact on the compressive strength of concrete was reported. At high replacement levels (12% and 50% PSA), a decrease in density
and strength was witnessed due to increased air content in concrete [9]. The use of mechanically-modified hydrophobic slag
was reported to reduce the early-age compressive strength by 15-30%, and an improvement in 28-day strength was found at
a cement replacement level of up to 10% by weight [26]. Shi et al. [46] reported a slight improvement in the compressive strength
of mortar treated with less than 10% chemically-modified hydrophobic slag due to the promotion of cement hydration. But
when the hydro- phobic slag was more than 10%, a larger required water-cement ratio and less cementitious material loosened the
internal structure of the mortar, which decreased the bearing capacity.
An improvement in compressive strength was also reported by the addition of some complex water-repellent modifiers, such
as
siloXane-based polymer (SP) and potassium trimethylsilanolate (PT) [75,76]. These hydrophobisation modifiers contain sour
tarring, sulphated melamine formaldehyde resins, soapstocks of vegetable oils, fly ash, triethanolamine, and fine rubber powder. A
concrete strength increase of 15-20% was reported after adding the modifiers. It was reported that the 28-day compressive strengths of
concrete increased from 39.6 to 45.8 and 42.l MPa when Conplast X421Ic and Conplast WP 90 (two commercial water-repellent
admiXtures) were used, respectively [63]. It is worth noting that the ingredients of those commercial products are not known.
Some crystalline admiXtures, such as sodium acetate, multi-crystallisation enhancers, silica-based crystalline admiXtures, and
LYN-
1 (a commercial cementitious crystallising material), may improve the concrete compressive strength at 28 days [52,58,77
]. For example, the compressive strength of concrete with 2% LYN-1 increased by 37% when the curing age increased from 7 to 28
days [52]. However, crystalline admiXtures were reported to work better for concrete with a low w/c ratio(≤ 0.37). At a high w/c
ratio ≥0.40, a strength loss of 20-30% (compared to the control concrete) has been reported by researchers when 2% and 4% silica-
based crystallising admiXture was used [63]. Al-Kheetan and Rahman [32] also reported a strength loss for concrete with a w/c ratio
≥0.40 after adding sodium acetate. A considerable reduction of 32% was reported for the 28-day compressive strength of a
miX (w/c ratio of 0.46) containing 4% sodium acetate compared with the reference concrete. In contrast, some other researchers
claimed that the addition of 3 to 4% sodium acetate into concrete with a w/c ratio of 0.54 had a negligible effect on the 28-
day compressive strength [78]. The authors added 4% sodium acetate by the weight of cement in concrete with a w/c ratio of 0.53
and found a slight strength increase of 5% at 28 days [10]. It seems that the fineness of sodium acetate powder and the dispersion
method might have an influence on the test results of cured samples. Due to the inconsistency of the results, further research is
required to understand the effect of sodium acetate on the concrete compressive strength. Commercially available crystalline
admiXtures (e.g. Xypex C-1000) have also been used by researchers. García-Vera et al. [79] reported that the addition of Xypex C-
1000 did not significantly affect the compressive strength of mortars in a non-aggressive environment. After 56 days of curing, the
compressive strength of mortar with 1% Xypex C-1000 reduced by 3% in comparison with the strength of the control mortar,
while mortar with 1.5 or 2% Xypex C-1000 experienced a strength increase by up to 28%. At 118 days, the difference in
compressive strength between the Xypex-treated and untreated mortars was within 2-10%. It is worth noting that the treated
mortar had a strength reduction of 7-20% when the curing age increased from 56 to 118 days. Another study found that the
compressive strength of Xypex-treated concrete decreased significantly (between 35 and 45%) when the curing age increased from
7 to 28 days [80]. The compressive strength of normal concrete is expected to increase with increasing curing age. As
ingredients in commercial products are not reported, it is hard to interpret their influence on concrete properties. There is no
comprehensive research on the effects of different waterproofing admiXtures on the compressive strength of concrete under
different curing conditions (e.g., water, air, and dry curing).
The above discussion shows that hydrophobic admiXtures often have a negative impact on the concrete compressive
strength,
causing a strength reduction of about 10% or more. This reduction is more noticeable at early ages (up to 28 days). The combined
use of these admiXtures with other materials, such as densifiers (e.g., SCMs), might be a good option to overcome the issue of
strength reduction; however, this needs further comprehensive research. The effect of crystalline waterproofing admiXtures on
the concrete compressive strength is somewhat inconclusive, especially in the case of using commercial crystalline admiXtures. As
the compressive strength of concrete is often considered to be the most critical factor in determining the quality of concrete
construction, trial tests on concrete miX with a new waterproofing admiXture are recommended before its practical applications.
2. Creep
Creep directly affects the concrete’s volume stability and leads to long-term deformation, internal stress redistribution,
and
prestress loss in prestressed concrete structures [89]. The creep behaviour of concrete with waterproofing admiXtures has seldom
been studied. Tkach et al. [75] presented experimental results of high-performance concretes with so-called hydrophobic
tragers and complex hydrophobisation modifiers. An increase of 10-20% was found for the creep deformation of all treated concrete
samples. The main reason for this is that the microparticles of surface-active substances were adsorbed on the surface of the
growing crystals hydrosilicate, leading to a formation of a microcrystalline structure for the cement hydrates [75]. More research
should be conducted to study the creep behaviour of concrete with other types of waterproofing admiXtures.
absorption of lightweight mortar by up to 90% [26]. Because of the use of lightweight aggregates (0.09-4 mm), the density of the
produced mortar was in the range of 1322-1430 kg/m3 . Although the reported reduction in capillary water absorption in Ref. [26]
was impressive, further research is required to study immersion water absorption of concrete with lightweight fine/coarse aggregate.
Meanwhile, further research could investigate the effects of type, porosity, size and morphology of aggregates on the performance of
waterproof concrete. Water absorption and sorptivity were reported to reduce by 83–84% and 83–86%, respectively, for concrete with
12% hydrophobic PSA compared to the reference concrete [9]. The effectiveness of hydrophobic PSA was proven for concrete even
after vacuum saturation and immersion in water for 40 days. Thus, the concrete with hydrophobic PSA showed resistance to hy-
drostatic pressure to some degree [9]. It should be noted the PSA was used as cement replacement in Ref. [9] when the w/c ratio was
kept constant. Hence, less water was used in concrete with PSA. Further research is required to investigate the effect of hydrophobic
PSA on the water absorption of concrete with the same amount of water.
Sodium acetate and silica-based crystallising agents were found to be effective in decreasing the water absorption of concrete
with
low w/c ratios of 0.32—0.37 [57,77,98]. Nevertheless, the authors [10] found that sodium acetate was also effective in
reducing the water absorption of concrete with a w/c ratio of 0.53 by about 50% after 60 days of curing. Some researchers have
studied the effect of commercially available crystalline admiXtures on the water absorption [79,80]. García-Vera et al. [79]
concluded that Xypex only slightly decreased mortars’ capillary water absorption. After the mortar samples were exposed to
sulphuric acid for 90 days, no meaningful difference was observed between the treated and untreated mortars in terms of water
absorption.
Different types of waste materials (such as waste glass, waste plastics, rubber tyres, and steel slag) can be used in concrete
as
aggregates or cement replacements. The impact of a particular waste material on the water absorption of concrete can vary
depending on the type and quantity of the waste material utilised. For example, glass powder can be used to develop ultra-
high performance concrete because its pozzolanic properties can be utilised to decrease the porosity of the concrete miX [99]. But the
porosity and water absorption of concrete could increase with increasing content of glass aggregates. Abdulkadir and
Mohammed [100] also reported inconsistent results regarding the effect of waste tires on the water absorption and permeability
of rubberised concrete. While some researchers reported that the water absorption of concrete increased with an increase in rubber
content, others reported the opposite [100]. Tian and Qiu [61] replaced 10—30% sand with crumb rubber by volume in making SCC.
The 48-h capillary water absorption of the reference SCC was reduced from 0.83% to 0.60% when the rubber content increased
from 0% to 30%. When 2% hydrophobic admiXture was added, the capillary water absorption values of SCC with 0% and
30% rubber were reduced by 71% and 65%, respectively. The crumb rubber was less effective in reducing capillary water
absorption of hydrophobic concrete than normal con- crete. Furthermore, it was found that the crumb rubber had negligible
influence on the 48-h immersion water absorption. It seems that caution must be exercised when using waterproofing admiXtures in
waste-based concrete.
This review shows that many hydrophobic and crystalline admiXtures can reduce the water absorption rate of concrete by up
to
80%. In practice, concrete can be exposed to either static or hydrostatic water pressure depending on the application scenario.
For example, concrete pavements are often subjected to static water pressure only from rainwater. The use of hydrophobic admiXtures
for concrete pavements is suitable, considering that these admiXtures often only reduce the water absorption under static water
pressure. When concrete is exposed to hydrostatic water pressure (such as in water tanks and swimming pools), the combined
use of hydro- phobic admiXtures with densifiers or crystalline admiXtures may be more suitable. More research is required to
completely understand the effects of different waterproofing admiXtures and their combined uses on the water absorption and
permeability of concrete under hydrostatic water pressure.
by either hydrophobic or crystalline admiXtures showed a reduced chloride ion penetration and improved chloride resistance to a
great extent. It may be inferred that there is a direct relationship between the water absorption rate and chloride resistance of
concrete. However, further research is required to establish such a relationship for different admiXtures.
4. Carbonation
Compared with the durability properties of integral waterproof concrete reviewed in previous subsections 4.4.1—4.4.3, much less
effort has been devoted to the study of other durability properties, such as carbonation, sulphate attack, acid attack, freeze-thaw
resistance, alkali silica reaction, efflorescence, abrasion resistance, and long-term durability.
Concrete carbonation is due to the penetration of carbon dioXide (CO 2) into the porous concrete, leading to a decrease in pH.
This
might accelerate chloride-induced corrosion of steel reinforcement [107]. Only a few studies have examined the
influence of waterproofing admiXtures on the carbonation resistance of concrete and mortar. Zhu et al. [54] studied the
carbonation rate of recycled aggregate concrete (RAC) treated with integral silane emulsion. The RAC had a w/c ratio of 0.5 and a
compressive strength of 37 MPa at 28 days. Silane emulsion was added to RAC at a dosage of 0.5% or 1% by cement weight. The
specimens were stored in a carbonation chamber with 4% CO 2. At 112 days, the carbonation depth of the RAC was about 20 mm,
which was two times that of the counterpart with natural aggregate. This is because RAC is more permeable than normal
concrete [108]. After adding 0.5% silane emulsion, the carbonation depth of the RAC was effectively reduced to 14 mm at 112
days. When the dosage of silane emulsion was increased to 1%, the carbonation depth dropped further to 12.5 mm. The slower
carbonation rate of concrete with silane emulsion could be explained by its lower water absorption [108]. Vikan and Justnes [109
] studied the influence of vegetable oils on mortar carbonation. The mortar had a w/c ratio of 0.5 and a cement-to-sand ratio of
1:3. The vegetable oil dosages were set to be 0.5%, 1.0% and 1.5% of cement weight. The carbonation of mortar samples in 5% CO 2
was monitored for 20 weeks. Surprisingly, it was reported that the addition of vegetable oils increased the carbonation depth of
mortar samples. Vikan and Justnes [109] attributed this to the increased amount of macro pores in mortar samples with vegetable
oils.
5. Sulphate attack 15
Sulphate attack is a complex damage phenomenon caused by the exposure of concrete to an excessive amount of sulphate from the
external environment or internal sources (such as sulphate present in the aggregates or binder). Sulphate can react with
calcium hydroXide (CH) and hydrated calcium silicate (C–S–H) in concrete to form expansive ettringite and gypsum, leading
S. Jahandari et al. Journal of Building Engineering 78 (2023) 107718
samples were cured for 28 days and then soaked for one year in sodium sulphate aqueous solutions with mass percentage concen-
trations of 2%, 5%, and 10%, respectively. It was found that the addition of PDMS significantly reduced the mortar strength. While
the reference untreated mortar had a 28-day compressive strength of 42.8 MPa, the corresponding strength of the PDMS-modified
mortar dropped to 22.4 MPa. As expected, the strength of the reference mortar decreased significantly with increasing soak time in
the sulphate solution, and the strength deterioration increased with increasing sulphate concentration. In contrast, the PDMS-
modified mortar did not demonstrate strength deterioration. The improved resistance of the PDMS-modified mortar to sulphate
attack was due to its reduced ingress of water and sodium sulphate [111].
used as the substrate pretreated with a silane coupling agent. The pretreated powder was then coated with a
polydimethylsiloXane modifier. YREC was added to concrete at a dosage of 2-4% by weight of cement. Unlike silane emulsion, YREC
was found to accelerate cement hydration. For this reason, adding YREC could increase concrete strength, especially at early ages.
After curing for 28 days, concrete samples were exposed to freeze-thaw cycles (—18 ◦C to +10 ◦C). The concrete failure was defined
as the moment when the loss in dynamic elastic modulus reached 60%. It was found that the reference concrete with a w/c
ratio of 0.5 failed after 35 freeze-thaw cycles. However, concretes with 2%, 3% and 4% YREC failed after 83, 89, and 111
freeze-thaw cycles, respectively. It appears that the addition of YREC improved the freeze-thaw resistance of concrete. Zhang et al. [
116] attributed this to the improved pore network after adding the admiXture, which reduced the water absorption by up to 18.5%.
More recently, Al-Kheetan et al. [57] studied the freeze-thaw performance of concrete with sodium acetate. Four concrete
miXtures
were developed with w/c ratios of 0.32, 0.37, 0.40, and 0.46, respectively. Sodium acetate was added at two different ratios: 2%
and 4% of cement weight. The freeze-thaw test was run for 6 months with temperatures changing from —10 ◦ C to +6 ◦ C. For concrete
with a low w/c ratio (0.32 or 0.37), the addition of sodium acetate improved its freeze-thaw performance, which was observed based
on the reduced concrete scaling and mass loss after testing. However, the inclusion of sodium acetate in concrete with a high w/c
ratio (0.40 or 0.46) reduced its freeze-thaw resistance. After adding 4% sodium acetate, the mass loss of the concrete with a w/c ratio
of 0.37 was about 4% when tested in water. But the corresponding mass loss of the concrete with a w/c ratio of 0.46 increased to
7.7%, which was even higher than the untreated concrete. Al-Kheetan et al. [57] explained that sodium acetate reduced the capillary
water in the concrete with a low w/c ratio, which improved its freeze-thaw resistance as capillary water is subjected to frost action.
However, sodium acetate increased microcracks and the content of air voids in concrete with a high w/c ratio, which reduced its
freeze-thaw resistance.
Research on freeze-thaw resistance of concrete with either hydrophobic or crystalline admiXtures has shown both positive
and negative impacts. Further comprehensive research is required to investigate the effect of combined use of different
waterproofing admiXtures on the freeze-thaw durability of concrete. In practice, air-entraining admiXtures are often used to improve
the resistance of concrete against freezing and thawing. The combined use of waterproofing and air-entraining admiXtures should
also be studied for practical applications.
9. Efflorescence
Efflorescence is the deposit of white salts (e.g., CaCO 3 , Na 2 CO 3 ) slowly migrating towards the concrete surface with the aid
of
moisture or water [120]. For OPC concrete, efflorescence is normally considered harmless except for a decline in aesthetic
appearance. But for geopolymer concrete (GPC) made with source material rich in silica and aluminium, efflorescence could be a
major issue due to the use of a large amount of water-soluble alkali activators. This is particularly a concern for conventional GPC
activated by sodium hydroXide and sodium silicate solutions. Efflorescence not only leads to inferior aesthetic appearance but also
structural damage to GPC [121].
Pasupathy et al. [122] used commercially-available hydrophobic fumed silica and silane cr`eme (a miXture of silane and siloXane)
to
control the efflorescence of GPC. They made hydrophobic sand first by coating the sand with 1—2% fumed silica or 10—20%
silane cr`eme by weight of the precursor (i.e., fly ash and slag). The treated sand was then added to the GPC miXture. After curing,
the GPC specimens were kept in contact with water at the bottom surface for 7 days to observe the formation of any
efflorescence. It was reported that the use of silane cr`eme reduced the compressive strength of GPC by up to 33% due to
the hindrance of the geo- polymerisation reaction. In contrast, the use of hydrophobic fumed silica enhanced the compressive
strength of GPC by up to 20% due to the filler effect. Meanwhile, all samples with hydrophobic sand had reduced surface-salt
accumulation because of reduced capillary water absorption and increased surface hydrophobicity of the GPC. In general,
hydrophobic fumed silica was more effective than silane cr`eme in controlling the efflorescence of GPC, because the former
could not only form hydrophobicity but also densify the micro- structure of GPC. The addition of 2% fumed silica completely
eliminated the formation of efflorescence in GPC.
Chindaprasirt et al. [120] made a lightweight fly ash-based geopolymer
17 cured at 65 ◦ C for 24 h. Fly ash was replaced by 1—10 wt
%
calcium stearate to increase hydrophobicity. The inclusion of calcium stearate in geopolymer slightly reduced its density (up to
14.8%) but significantly reduced its strength. The reference geopolymer and the one with 10% calcium stearate had compressive
S. Jahandari et al. Journal of Building Engineering 78 (2023) 107718
immersed in water for 24 h. This is due to the increased pores in geopolymer with the addition of calcium stearate.
However, by incorporating 5% or 10% calcium stearate into the miXture, the issue of efflorescence was effectively eliminated.
127]. However, a single waterproofing admiXture would be very challenging to meet the many design requirements for
concrete durability, such as chloride penetration, reinforcement corrosion, and carbonation. It is an interesting idea to combine
admiXtures with different mechanisms of waterproofing, but very little research has been conducted in this direction. Al-Rashed
and Al-Jabari [58] developed a multi-crystallisation admiXture, which combines hygroscopic and hydrophilic crystals with a
hydrophobic characteristic. Some manufacturers also claim that their products have both hydrophobic and crystalline
compounds [126]. However, vigorous research is required to check the effects of such complex admiXtures on the fresh,
mechanical, and durability properties of concrete. Currently, there is a lack of guidelines to determine the efficacy of waterproofing
admiXtures, and the sample preparation processes are also not consistent. Researchers tend to make concrete with a specific
w/c ratio and then vary the dosage of a waterproofing admiXture. But different practices have been adopted in demoulding
(with or without demoulding agents), curing (controlled or uncontrolled conditions), and drying (temperature and duration)
their concrete samples [128]. The efficacy of the waterproofing admiXture is often judged by the reduction in water absorption,
which is relatively easy to measure. Since the concrete miX designs and test procedures are often different, it is not straightforward to
compare the test results in different studies. While water absorption is an important parameter, the effects of waterproofing
admiXtures on some important durability properties (e.g., reinforcement corrosion,
carbonation, acid resistance) should also be tested to judge the efficacy of the admiXtures.
Most of the previous studies have focused on the compressive strength and water absorption of integral waterproof concrete,
and
limited efforts have been devoted to investigating its durability properties. Meanwhile, the toXicity and environmental
impact of waterproofing admiXtures should also be studied. In particular, there is a lack of long-term field monitoring of
integral waterproof concrete. When using waterproofing admiXtures, a premium needs to be paid, which increases the construction
cost. Due to inadequate research on the durability of integral waterproof concrete, it is not possible to accurately predict the
increase in the service life of concrete structures and infrastructure for the use of waterproofing admiXtures. Further research is
required to assess the long-term benefits of using integral waterproof concrete based on life cycle assessment.
Previous studies have mainly focused on OPC concrete. In recent years, alkali-activated concrete (e.g., GPC) has been attracting
increasing research interest as a promising alternative to OPC concrete to reduce carbon emissions from construction activities [129].
A few studies [130] have been conducted to treat GPC with a surface coating to reduce its water absorption. However, very
little attention has been paid to developing waterproof alkali-activated concrete [122]. It should be noted that waterproofing
admiXtures developed for conventional OPC concrete might not work in alkali-activated concrete. For instance, sodium acetate has
been recog- nised as an effective waterproofing admiXture for OPC concrete [10]. However, it cannot be used in GPC due to the
chemical reaction between the sodium acetate and sodium hydroXide in the miXture; the reaction produces methane and
generates pores inside the concrete. Further work is required to develop waterproof alkali-activated concrete with high
performance and cost effectiveness.
6. Conclusions
This paper has conducted a comprehensive review of integral waterproof concrete. Mechanisms and limitations of different types
of waterproofing admiXtures were reviewed first. Then the effects of waterproofing admiXtures on the concrete’s fresh, mechanical
and durability properties were summarised. Finally, challenges and future perspectives in developing integral waterproof concrete
were presented. The following conclusions can be drawn from this study:
(1) Waterproofing admiXtures can be roughly classified into three groups: densifiers, water repellents, and crystalline admiXtures.
Because of the limited efficacy, densifiers cannot be used alone to develop waterproof concrete. Water repellents are suitable
for non-critical areas with low water tables or above-ground applications. Crystalline admiXtures can form crystals in concrete
with pore-blocking effects and are suitable for structures under hydrostatic conditions. Currently, there is a trend to develop
ad- miXtures with hydrophobic and crystalline compounds. But rigorous research is required to check their effects on different
concrete properties.
(2) Water repellents tend to reduce concrete strength, which is especially true for silane/siloXane-based products. To
compensate
for the strength loss, a suitable amount of densifiers, such as supplementary cementitious materials, can be added to
the concrete miXture. The effect of crystalline admiXtures on the concrete compressive strength is somewhat
inconclusive, espe- cially in the case of using commercial crystalline admiXtures.
(3) Waterproofing admiXtures have a tendency to reduce drying shrinkage and plastic shrinkage of concrete.
(4) Researchers have consistently reported the reduction of concrete water absorption by up to 80% after using waterproofing
admiXtures. They also reported reduced chloride penetration in integral waterproof concrete. However, contradictory results
have been reported on reinforcement corrosion. For uncracked concrete, waterproofing admiXtures are effective in protecting
steel reinforcement from corrosion. But the efficacy of waterproofing admiXtures is questionable for cracked concrete.
(5) Integral waterproof concrete might have increased resistance to carbonation, provided that the waterproofing admiXture does
not negatively affect the microstructure.
(6) The addition of waterproofing admiXtures can improve the freeze-thaw resistance of concrete, provided that the concrete
strength is not significantly reduced. Furthermore, waterproofing admiXtures also have the potential to mitigate alkali-silica
reaction and efflorescence of concrete.
It is worth noting that reports on the efficacy of commercial waterproofing admiXtures are inconsistent. More research is required
to develop economical and effective waterproofing admiXtures, which will increase the confidence of the construction industry
in waterproofing admiXtures. Meanwhile, there is a need to develop19 proper guidelines on sample preparation and determination of
the efficacy of waterproofing admiXtures. The toXicity and environmental impact of waterproofing admiXtures should also be
studied.
S. Jahandari et al. Journal of Building Engineering 78 (2023)
107718
Further work is required to develop waterproof alkali-activated concrete with high performance and cost-effectiveness. Moreover, the
effect of waterproofing admiXtures on the concrete creep has seldom been studied. Only one study reported an increase of 10-20% in
creep for their hydrophobic concrete. Very limited studies have been conducted on integral waterproof concrete subjected to sulphate
or acid attack. It appears that the integral waterproof concrete has improved resistance to chemical attacks. However, it is inconclusive
in terms of the microbial-induced corrosion of integral waterproof concrete when used in concrete sewer systems. Further research is
required in this area. Finally, very limited research has been conducted on the long-term performance of integral waterproof concrete
in both laboratory and field, and the reported conclusions are contradictory. Therefore, further research is required to assess the long-
term benefits of using integral waterproof concrete based on life cycle assessment.
Data availability
Acknowledgements
The authors gratefully acknowledge the financial support of the Australian Research Council Research Hub for Nanoscience
Based Construction Materials Manufacturing (IH150100006).
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