WO2004080912A1

WO2004080912A1 - A method for producing structural lightweight aggregate concrete

Info

Publication number: WO2004080912A1
Application number: PCT/SE2004/000353
Authority: WO
Inventors: Johnny Johansson
Original assignee: Johnny Johansson
Priority date: 2003-03-10
Filing date: 2004-03-10
Publication date: 2004-09-23
Also published as: SE524924C2; SE0300633L; SE0300633D0

Abstract

A method for manufacturing self compacting and other structural lightweight aggregate concrete in the density interval of 800 - 1800 kg /M3 by, in a first step, mortar is mixed using Portland cement and/or another type of cement, water, admixtures, natural rock-type aggregates and filler in the density interval above 2 000 kg/m3, and, in a second step, adding lightweight aggregates. Rock-type aggregates having a maximum particle size of 8 mm are used in the mortar. The mortar paste volume comprising cement, water, air and the part of aggregates and filler passing through a 0.25 mm sieve is adjusted to at least 45 vol.% of the total concrete volume and at least 60 vol.-% of the total mortar volume. The yield stress τ0 of the mortar is adjusted to a value within the interval 10 - 600 Pa, the plastic viscosity μm of the mortar is adjusted to 0,5 - 35 Pa.s. Lightweight aggregate is added so that its volume is 20 - 45 vol.-% of the total concrete volume.

Description

A METHOD FOR PRODUCING STRUCTURAL LIGHTWEIGHT AGGREGATE CONCRETE

The present invention relates to a method for manufacturing structural lightweigt aggregate concrete, and particularly in the density range from 800 to 1800 kg/m³. According to a specific embodiment the invention relates to self-compacting structural lightweight aggregate concrete.

Prior art A common problem in structural lightweigt aggregate concrete is the segregation of lightweight aggregate particles in the fresh concrete during transport as well as in the casting process. Lightweight aggregate particles having a lower density than the surrounding matrix, i.e. the paste or mortar, strive to move upwards towards the surface. Segregating concrete will lead to a non-homogenous structure resulting in low strength values. There is also a risk that the increased concentration of lightweight aggregate volume in the upper parts of the concrete leads to a cavity-containing structure. In order to solve of the above problems a number of methods in the prior art are used:

1. Minimizing the differences in density between the mortar matrix and the lightweight aggregate grains.

2. Limiting the maximum grain size of the lightweight aggre- gate grains.

3. Assembling the total aggregate material (aggregate material in the mortar + the lightweight aggregates) so that a continuous particle distribution is achieved (a so called modified Fuller curve) . 4. Avoiding low plastic viscosity consistencies.

In real cases, with the aggregate materials being offered today, it might be difficult to achieve the desired aggregate properties .

In reality it will be impossible to obtain the desired den- sity of the concrete without using lightweight aggregates with a density substantially deviating from the density of the mortar matrix.

Due to the sensitivity of the ligthweight aggregate con- crete to different compaction methods, e.g. rod vibration, in many cases it is necessary to reduce the need of compaction work and thus, to increase concrete flowability or to make the concrete self-compacting.

Admixtures used are often specifically adjusted for light- weight aggregate concrete and are in many cases difficult to use in practise. The above conditions often make it difficult to get the structural lightweight aggregate concrete economically competitive.

In addition, problems occur when structural lightweight aggregate concrete is to be produced using conventional technology in a ready-mix plant. Normally a large amount of different concrete batches are mixed in one and the same mixer during a work shift in order to use the plant efficiently. If lightweight aggregates are introduced into the mixer an efficient cleaning of the mixer is necessary before the next normal concrete batch- can be mixed together therein. The reason for this is that it is not acceptable for lightweight aggregates to end up in the normal concrete. Such a cleaning process is most often impossible to perform during production. Therefor, structural lightweight aggregate concrete is not allowed into normal concrete plants, and thus necessary to be produced in specially designed plants, which adds substantially to the costs for this concrete.

The above noted problems can be solved with the method according to the invention for producing structural lightweight aggregate concrete.

Short description of the invention

The object of the invention is to provide a method making it possible to prevent lightweight aggregate particles from seg- regation in the fresh concrete mass during production, transportation as well as during a casting process when using structural lightweight aggregate concrete.

This is achieved with the method according to the present invention, wherein self-compacting and other structural lightweight aggregate concrete in the density interval of 800 - 1800 kg/m³ is produced by in a first step dressing a mortar of Portland cement and/or another cement type, water, additives, natural rock-type aggre- gates and filler in the density interval above 2 000 kg/m³, and in a second step adding lightweight aggregates, characterized by using rock-type aggregates, having a maximum particle size of 8 mm in the mortar, - adjusting paste volume of the mortar consisting of cement, water, air and the part of aggregates and filler passing a 0.25 mm sieve to least 45 vol.-% of the total concrete volume and at least 60 vol.-% of the total mortar volume, adjusting the yield stress τo to a value within the inter- val 10 - 600 Pa, adjusting the plastic viscosity of the mortar μ_m to 0,5 - 35 Pa.s, and adding lightweight aggregates so that the total lightweight aggregate volume amounts to 20 - 45 vol.-% of the total concrete volume.

According to one embodiment of the invention the rock-type aggregates and the filler are adjusted so that 25 - 5 vol.-% of the particles pass a 0.063 mm sieve, 32 - 7 vol.-% of the particles pass a 0.125 mm sieve, 45 - 16 vol.-% of the particles pass a 0.25 mm sieve, 60 - 28 vol.-% of the particles pass a 0.5 mm sieve, 75 - 47 vol.-% of the particles pass a 1.0 mm sieve, 90 - 65 vol.-% of the particles pass a 2.0 mm sieve, 100 - 80 vol.-% of the particles pass a 4.0 mm sieve, 100 - 90 vol.-% of the particles pass a 8.0 mm sieve, the yield stress τ₀ is adjusted to a value within the interval 10 - 300 Pa, and the plastic viscosity μ_m is adjusted to within the interval 0.5 - 8.0 Pa. s.

According to another embodiment of the invention the rock- type aggregates and the filler are adjusted so that 100 - 25 vol.-% of the particles pass a 0.063 mm sieve, 100 - 32 vol.-% of the particles pass a 0.125 mm sieve, 100 - 45 vol.-% of the particles pass a 0.25 mm sieve, 100 - 60 vol.-% of the particles pass a 0.5 mm sieve, 100 - 75 vol.-% of the particles pass a 1.0 mm sieve, 100 - 90 vol.-% of the particles pass a 2.0 mm sieve, 100 - 100 vol.-% of the particles pass a 4.0 mm sieve, - the yield stress To is adjusted to a value within the interval 15 - 45 Pa, and the plastic viscosity μ_m is adjusted to within the interval 1.0 - 10.0 Pa.s.

According to still another embodiment of the invention the rock-type aggregates and the filler are adjusted so that 25 - 5 vol.-% of the particles pass a 0.063 mm sieve, 45 - 10 vol.-% of the particles pass a 0.125 mm sieve, 95 - 47 vol.-% of the particles pass a 0.25 mm sieve, 100 - 78 vol.-% of the particles pass a 0.5 mm sieve, 100 - 90 vol.-% of the particles pass a 1.0 mm sieve, 100 - 100 vol.-% of the particles pass a 2.0 mm sieve, the yield stress τ₀ is adjusted to a value within the interval 20 - 40 Pa, and the plastic viscosity μ_m is adjusted to within the interval 1.0 - 15.0 Pa.s.

According to still another embodiment of the invention sand with a rounded grain form is used as rock-type aggregates, or re-circulated sand from metal casting procedures and/or residual material from mineral processing. According to still another embodiment of the invention the following materials are used as fillers; any type of recovered material, such as finely ground, re-circulated glass, residual materials from mineral processing and/or finely ground limestone filler.

According to still another embodiment of the invention the following materials are used as lightweight aggregates; recovered EPS plastic, expanded glass lightweight aggregates manufactured from recovered glass, expanded polystyrene, PVC granules, recovered pelletized PET material and/or expanded clay such as Leca, Liapor, Lytag.

According to still another embodiment of the invention the following materials are used as lightweight aggregates; grains either with a uniform grain size and grain form or varying grain sizes and grain forms, whereby the grains may consist of only one kind of material or of a mixture of materials with different densities and surface properties.

According to still another embodiment of the invention all constituents, except water, for the mortar are dosed, wrapped and distributed in dry form to the mixing site where they will be mixed with water to form the mortar.

According to the invention a mortar with known rheological properties, yield stress, plastic viscosity is prepared and thereafter the desired lightweight aggregate is added. Putting together a size distribution curve for generally occurring rock- type aggregates according to the claims in the present patent application is fairly easy, and producing a mortar according to the claims in this patent application can be done according to known technology. The completed mortar can then be supplemented with the appropriate amount and quality of lightweight aggregates in order to obtain the desired properties of the structural lightweight aggregate concrete, such as density and strength.

In one embodiment of the invention the same mix design of the mortar and the same lightweight aggregates can be used to provide a concrete with a bulk density of 990 kg/m³, as well as a concrete with a bulk density of 1770 kg/m³. The difference lies in different amounts of air and plasticizers and the amount of lightweight aggregates. Maximum particle size of the rock-type aggregates is 8 mm and the lightweight aggregates consist only of polystyrene foam plastic.

In another embodiment of the invention 2 mm is used as the maximum particle size of the rock-type aggregates and Leca 2-6 mm and Leca 4-10 mm as lightweight aggregates. Concrete slump flow was 800 mm, compressive strength 32 MPa and density 1550 kg/m³.

In still another embodiment of the invention 0.5 mm is used as maximum particle size of the rock-type aggregates and with only recovered EPS as lightweight aggregates. Concrete slump flow was 750 mm, compressive strength 12 MPa and density 1350 kg/m³.

Short description of the drawings

The invention will be described more in detail below with reference to a number of embodiments and the accompanying drawings, wherein:

Fig. 1 describes the area within which the particle size distribution (PSD-) curves for rock-type aggregates + filler should be according to claim 2. The curves A and B define the outer limits of the area in question. The curves 1- 2 and 3 are PSD-curves for the rock-type filler materials used in mortar A - J, shown in Figure 4 and 5.

Fig. 2 describes the area within which the PSD-curves for rock-type aggregates + filler should be according to claim 3. Curve B is the lower limit for the area in question. Curves 4, 5 and 6 are PSD-curves for the rock-type filler materials used in mortar K - N, shown in Fig. 6. Fig. 3 describes the area within which the PSD-curves for rock-type aggregates + filler should be according to claim 4. The curves C and D are outer limits for the area in question. The curves 7, 8 and 9 are PSD-curves for the rock-type filler materials used in mortars 0 - V shown in Fig. 7.

Fig. 4 describes diagrammatically the rheological values yield stress and plastic viscosity for mortars A - F.

Fig. 5 describes the rheological values yield stress and plastic viscosity for mortars G - J.

Fig. 6 describes the rheological values yield stress and plastic viscosity for mortars K - N.

Fig. 7 describes the rheological values yield stress and plastic viscosity for mortars 0 - V.

Detailed description of the inventio .

The invention will now be described below with reference to the accompanying drawings. In the present specification, in the claims and on the drawings certain technical terms _are used. These might be well known for the man skilled in the art, but in order to avoid misunderstandings the following explanations are offered. "The slump flow value" describes the flowability of the concrete, which, to a certain extent is inversly proportional to the yield stress of the concrete. It is measured by filling concrete into a so called slump cone. When the slump cone is lifted the concrete flows out freely on a base plate, and the slump flow value is the final concrete spread diameter in mm for the flown-out concrete. The "slump value" (SS EN.206-1) is the distance in mm the concrete sets when a slump cone according to the above is lifted. The yield stress τ₀ is the shear stress the con- crete has to be subjected to in order to start to flow. Self- compacting concrete is rheologically characterized by a low yield stress and a relatively high plastic viscosity. The plastic viscosity describes concrete flow characteristics when flow- ing (stress is higher than τ₀ ) .

In a first step the mortars to be included in the final concretes are prepared, complete with the PSD-curves and rheological properties according to claims 1 - 4.

In a second step the chosen lightweight aggregates are added in the amount which has been tested out for providing a concrete with the desired rheology and strength. This second step could advantageously be taken after having discharged the mortar into a concrete truck of a so called rotating type, whereupon the lightweight aggregates are mixed into the mortar during the drive to the working site. Thus, the problem with lightweight aggregates in the concrete mixer at the ready-mix plant can be solved.

The lightweight aggregates might have a wide variety of characteristics, and it could for example consist of recovered EPS plastic, expanded glass lightweight aggregates produced from recovered glass, expanded polystyrene, PVC granules, recovered pelletized PET material, expanded clay, e.g. Leca, Liapor, Ly- tag. No specific demands are put on the grain density and PSD- curve for the lightweight aggregates. The fresh concrete properties have successfully been tested in the range from a slump-flow value of 20 mm to a slump-flow value of 800 mm.

The admixtures used are air entraining agents and plasti- cizers which are common in the market. The materials contained in the mortars can also be variated within a large interval, such as the normallhy used 0 - 8 mm concrete aggregate together with limestone filler, which comprise the rock-type aggregates in PSD-curve 1 in Fig. 1 and are contained in mortars A to F in Fig. 4 and concretes based on these mortars. These materials are available in all concrete ready-mix plants and the air entraining agents and plasticizers used in the normal production, can also be used for the mortar of the structural lightweight aggregate concrete. The concrete with mortar C as a base had a slump-flow value of 445 mm, which can be regarded as a self-compacting structural lightweight aggregate concrete. The concrete with mortar D as a base had a slump-flow value of 60 mm, which is on the edge of plastic consistency. The PSD-curves 2 and 3, shown in Fig. 1 represent crushed stone fines with maximum particle size d_max. = 4 mm and two different filler additives. Mortar produced with these rock-type aggregates are shown in Fig. 5.

An example of the extreme towards finer particle sizes of rock-type aggregates is shown with PSD-curve 6 in Fig. 2. This is a limestone filler material with d_max. = 0,1 mm. This material is used in mortar N, shown in Fig. 6. The concrete with mortar N as a base had a slump-flow value of 780 mm. Production of concrete with mortar N as a base is technically easy but it is more difficult to make economically feasible. It might be possible to use residual products from mineral processing making it economically more interesting.

The PSD-curves shown in Fig. 3 represent rock-type aggregates being advantageous both from technical and economical viewpoints. PSD-curve 9 in Fig. 3 shows a naturally occurring sand without filler additive and PSD-curve 8 in Fig. 3 shows a rock-type aggregate with a small addition of filler material. The mortars R and S in Fig. 7 resulted in concretes with slump flow values of 550 and 430 mm, respectively and a density of 1360 kg/m³ concrete. PSD-curve 7 in Fig. 3 can be regarded as an optimized rock-type aggregate composition including filler and is used in mortar Q which is shown in Fig. 7. The concrete with mortar Q as a base got a slump-flow value of 455 mm and a density of 1200 kg/m³.

Claims

1. A method for producing self-compacting and other structural lightweight aggregate concrete in the density interval of 800 - 1800 kg/m³ by - in a first step mixing a mortar of Portland cement and/or another type of cement, water, admixtures, natural rock-type aggregates and filler in the density interval above 2 000 kg/m³, and in a second step adding lightweight aggregates, characterized by using a rock-type aggregate having a maximum grain size of 8 mm in the mortar, adjusting the mortar paste volume comprising cement, water, air and the part of aggregates and filler passing through a 0.25 mm sieve spacing, so that it comprises at least 45 % of the total concrete volume and at least 60 % of the total mortar volume, adjusting the yield stress τo of the mortar to a value within the interval 10 - 600 Pa, - adjusting the plastic viscosity μ_m of the mortar to 0,5 - 35 Pa.s, and adding lightweight aggregates so that the total lightweight aggregate volume amounts to 20 - 45 vol.-% of the total concrete volume .

2. A method according to claim 1, characterized by adjusting the rock-type aggregates and the filler so that

25 - 5 vol.-% of the particles pass a 0.063 mm sieve, 32 - 7 vol.-% of the particles pass a 0.125 mm sieve, 45 - 16 vol.-% of the particles pass a 0.25 mm sieve, 60 - 28 vol.-% of the particles pass a 0.5 mm sieve, 75 - 47 vol.-% of the particles pass a 1.0 mm sieve, 90 - 65 vol.-% of the particles pass a 2.0 mm sieve, 100 - 80 vol.-% of the particles pass a 4.0 mm sieve-, 100 - 90 vol.-% of the particles pass a 8.0 mm sieve, adjusting the yield stress τ₀ to a value within the inter- val 10 - 300 Pa, and adjusting the plastic viscosity μ_m to a value within the interval 0.5 - 8.0 Pa.s.

3. A method according to claim 1, characterized by - adjusting the rock-type aggregates and the filler so that 100 - 25 vol.-% of the particles pass a 0.063 mm sieve,

100 - - 32 vol -% of the particles pass a 0.125 mm sieve,

100 - - 45 vol -% of the particles pass a 0.25 mm sieve,

100 - - 60 vol -% of the particles pass a 0.5 mm sieve,

100 - - 75 vol -% of the particles pass a 1.0 mm sieve,

100 - - 90 vol -% of the particles pass a 2.0 mm sieve, 100 - 100 vol.-% of the particles pass a 4.0 mm sieve, adjusting the yield stress τo to a value within the interval 15 - 45 Pa, and - adjusting the plastic viscosity μ_m to a value within the interval 1.0 - 10.0 Pa.s.

4. A method according to claim 1, characterized by adjusting the rock-type aggregates and the filler so that 25 - 5 vol.-% of the particles pass a 0.063 mm sieve, 45 - 10 vol.-% of the particles pass a 0.125 mm sieve, 95 - 47 vol.-% of the particles pass a 0.25 mm sieve, 100 - 78 vol.-% of the particles pass a 0.5 mm sieve, 100 - 90 vol.-% of the particles pass a 1.0 mm sieve, 100 - 100 vol.-% of the particles pass a 2.0 mm sieve, adjusting the yield stress τo to a value within the interval 20 - 40 Pa, and adjusting the plastic viscosity μ_m to a value within the interval 1.0 - 15.0 Pa.s.

5. A method according to claim 1, characterized by using sand with a rounded grain form, or recirculated sand from metal casting procedures and/or residual materials from mineral processing, as rock-type aggregates.

6. A method according to claim 1, characterized by using as fillers any type of recovered material, such as finely ground, recovered glass, residual materials from mineral processing and/or finely ground lime filler.

7. A method according to claim 1, characterised by using as lightweight aggregates recovered EPS plastic, expanded glass lightweight aggregates manufactured from recovered glass, expanded polystyrene, PVC granules, recovered pelletized PET material and/or expanded clay, such as Leca, Liapor, Lytag.

8. A method according to claim 1, characterised by using as lightweight aggregates grains either with uniform grain size and grain form or varying grain sizes and grain forms, whereby the grains may consist of only one kind of material or of a mixture of materials with different densities and surface properties.

9. A method according to claim 1, characterised by dosing, wrapping and distributing all ingredients, except water, for the mortar in dry form to the mixing site, whereat they will be mixed with water when the mortar is dressed.