Journal of Colloid and Interface Science
Journal of Colloid and Interface Science
Journal of Colloid and Interface Science
a r t i c l e i n f o a b s t r a c t
Article history: Hydration phenomena at cement/water interfaces drive the characteristics of oil-well cement slurries. In
Received 23 September 2009 this study, new epoxy-modied cement slurries were synthesized. The slurries characterization has sug-
Accepted 5 November 2009 gested the presence of low amounts of portlandite in the slurry with the higher content of polymerized
Available online 18 November 2009
epoxy resin. The hydration processes of the cement slurries were studied by heat-conduction microcal-
orimetry. The energetic and enthalpic hydration data were all exothermic in nature. The cumulative heat
Keywords: release curves have shown the presence of multilinearity of the kinetic processes. The hydration micro-
Cement/water interfaces
calorimetric data were well tted to the multistep Avrami kinetic model. It was found that the epoxy-
Oil-well cement slurries
Epoxy resins
modied cement slurries present a good potential to be used in environmental-friendly oil-well
Microcalorimetry operations.
Thermodynamics 2009 Elsevier Inc. All rights reserved.
Kinetics
1. Introduction slurries [8]. Currently almost 90% of the world production of epoxy
resins is based on the reaction between bisphenol A (2,2-bis(40 -
Portland cement is used in large quantities to grout oil-wells. hydroxyphenyl)propane and epichlorohydrin 24 [9]. Epoxy ce-
The cement slurry is placed between a metal liner and the walls of ment mortars are composed of emulsied bisphenol A epoxy resin,
the borehole to provide support for the liner and a seal to prevent cement, and ne aggregates. In some cases, the epoxy cement mor-
the migration of gas and loss of zonal isolation along the outside of tars with hardeners, which are Lewis bases in nature (generally, or-
the liner [1]. Long-term performance of the cement slurries is of ganic acids or amines), have some properties that are better than
great concern. If the cement slurry does not provide a good seal, the mortars without a hardener. The conventional epoxy cement
loss of zonal isolation leads to safety and environmental problems mortars with a hardener must have a polymer content higher than
[13]. 40% to achieve good mechanical properties and durability. The
Portland cements withstand chemical (dissolution and precipi- epoxy resins can also harden in the presence of alkalis formed from
tation) and physical (occulation and coagulation) changes when the hydration of cement [10].
in contact with water [4]. Such changes have signicantly affected The hydration of cementitious materials is exothermic, with en-
the rheology of hydrating cementitious materials since the early ergy of up to 100 J/g of cement being liberated [11]. The knowledge
ages, even during the induction period, when the hydration reac- of the heat-producing properties of different cementitious materi-
tions are still incipient. When chemical admixtures are present, als is required in order to choose a suitable cementitious system
the system becomes even more complex due to physicalchemical for a given specic project. The kinetic and thermodynamic fea-
interactions with the hydrating cement [5]. The protective charac- tures of the early hydration stages are essential for the perfor-
teristics of oil-well cements are in practice controlled by the addi- mance of hardened cements and can be monitored by isothermal
tion of polymeric additives [6]. microcalorimetry [12]. However, there is relatively little research
Water-soluble polymers are frequently added to cement mor- on early cement hydration, that is, the initial hours after adding
tars in order to improve the fresh mixture properties [7]. Epoxy water.
resins are used to provide a good wettability of the cementitious In this work, two epoxy-modied cement slurries and an epoxy-
substrate. Polymeric epoxy resins have been useful in promoting free cement slurry were obtained and characterized. Heat-conduc-
the physico-chemical interactions and ensure an optimal level of tion microcalorimetry was used to obtain and to compare the fea-
adhesion between the mineral and the organic phases of cement tures of heat evolution evolved in the early stages of hydration of
the epoxy-modied cement slurries, with the objective of increas-
ing the understanding of the hydration processes at cement/water
* Corresponding author. Fax: +55 79 21056684.
E-mail address: cestari@ufs.br (A.R. Cestari).
interfaces.
0021-9797/$ - see front matter 2009 Elsevier Inc. All rights reserved.
doi:10.1016/j.jcis.2009.11.017
A.R. Cestari et al. / Journal of Colloid and Interface Science 343 (2010) 162167 163
2. Materials and methods range from 5 to 80 (accumulation rate of 0.02 deg min1), using
Cu Ka radiation.
2.1. Materials and reagents
Water was double-distilled before use. Powder cement (200 2.4. Microcalorimetric experiments
325 mesh, Class A) from Cimesa (Laranjeiras-SE, Brazil) was used.
The characteristics of the cement powder were shown earlier Microcalorimetric measurements of the hydration processes of
[10]. The bisphenol F epoxy resin, commercially available as Aral- the slurries were performed at 25 C in a SETARAM C80 heat-con-
dite PY340, and its hardener (Versamid 125) were supplied by duction calorimeter (France). Specic characteristics of the heat-
The Huntsman Co. Special Resins. The chemical structures of the conduction calorimetric system have been previously described
resin and the hardener are shown in Fig. 1. [13,14]. In a typical experiment, a cementitious conical sample
was put into the lower part of the calorimetric cell closed by a cir-
cular PTFE thin membrane. Into the upper part of mixing cell, a vol-
2.2. Preparation of the cement slurries ume of 3.0 ml of water was added. After complete stabilization of
the calorimeter base line, a movable rod enables water to be
The mixing procedure adopted was in accordance with the Amer- pushed into the container with the cementitious sample. Each indi-
ican Petroleum Institute (API) practice, and consisted of mixing the vidual experiment yields a thermal effect, Qr. Data acquisition was
cement, epoxy resin, and hardener at 4000 rpm for 20 s, and then continued for nearly 160 h. The thermal effect of membrane break-
mixing for 30 s at 12,000 rpm [10,13]. Two epoxy-modied slurries ing for the empty cell was found to be negligible compared to Qr
were synthesized using 10% and 30% of the epoxy resin in relation to values. The detectable calorimeter signals (power versus time), as
the cement mass. In order to avoid uncompleted polymerization, the well as the cumulative heats of hydration were performed using
proportion of epoxy resin/hardener was 1/2. The cement and water the SETSOFT software (SETARAM). Each experiment was repeated
were used to obtain the standard cement slurry. The amounts of the at least in duplicate. Statistical calculations (t tests, F tests, analysis
components of the slurries were calculated in relation to a nal den- of variance (ANOVA), and multiple regressions) were carried out
sity of the cured slurries from 1.50 to 2.00 g cm3 [10,13]. The ce- with ORIGIN and Statistica softwares, both releases 7.0.
ment slurries were cast into cylindrical molds with each
10.0 20.0 mm for 6 h at room temperature before use. The slurries
are hereafter denominated, for simplicity, as standard slurry (ce- 3. Results and discussion
ment and water), PY340-1 (30% of Araldite PY340 + hardener), and
PY340-2 (10% of Araldite PY340 + hardener). 3.1. Some initial considerations
CaO H2 O ! CaOH2 1
The alkali metal ions from the sulfates readily enter the solution
Fig. 1. Chemical structures of the epoxy resin (above) and the hardener (below). when the cement is mixed with water and accelerate the early
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