CASTABLE MATERIAL BASED ON CEMENTITIOUS MATERIAL WITH SHRINKAGE RESISTANCE

Abstract

Some embodiments are directed to a new castable cement based material containing a special admixture based internal curing system to reduce the shrinkage and avoid the formation of cracks, and method of producing the same.

Claims

1. A cementitious material mix design, comprising: (a) a cementitious binder that contains an Ordinary Portland Cement, the binder content per cubic meter of fresh produced castable material (concrete or mortar) being at least 290 kg; (b) sand, the sand content per cubic meter of fresh concrete or mortar being between 500 kg and 1600 kg; (c) water, wherein the water to total binder ratio is between 0.25 and 0.7 by weight; (d) a self-curing system; and (e) a volume of paste in an amount of at least 250 l per cubic meter of fresh concrete or mortar; wherein, the internal curing system includes a mixture of a superabsorbent polymer, a viscosity modifier and an inorganic salt, in water.

2. The cementitious material mix design according to claim 1, further comprising fine and/or coarse aggregates.

3. The cementitious material mix design according to claim 1, wherein the internal curing system is present in an amount so that the dry solid content of the internal curing system is between 0.2% and 2.2%, wherein the dry solid content is expressed in weight % with respect to the total binder.

4. The cementitious material mix design according to claim 1, wherein the internal curing system comprises between about 40 M.-% and 70% M.-% of water, between about 0.05 M.-% and 0.5 M.-% of viscosity modifier, between about 10.0 M.-% and 30.0 M.-% of inorganic salt between about 5.0 M.-% and 20.0 M.-% of superabsorbent polymer.

5. The cementitious material mix design according to claim 1, wherein the viscosity modifier agent is chosen from polysaccharides, polymers of acrylic acid and co-polymers thereof, polyethylene and related copolymers, alkylene oxide polymers and esters thereof, and methyl vinyl ether/maleic anhydride copolymers crosslinked with decadiene.

6. The cementitious material mix design according to claim 1, wherein the cation of the inorganic salt has a valence between 1 and 3.

7. The cementitious material mix design according to claim 1, wherein the superabsorbent polymer in the internal curing system is a potassium-based superabsorbent.

8. A method of using an aqueous suspension of super absorbent polymer for increasing shrinkage resistance of cementitious material mix design.

9. A method for producing a stable aqueous suspension of super absorbent polymer, comprising: mixing a viscosity modifier agent with water; adding a suitable inorganic salt and mixing for a time t that is at least 30 minutes; and adding the superabsorbent polymer to form an aqueous suspension.

Description

EXAMPLES

[0110] Examples 1-7 are provided for concrete screed and mortar according to the first and second embodiment of the presently disclosed subject matter and mortars (respectively using the components of the internal curing system formulated in an admixture).

[0111] The cements used are of type Portland cement type I, II (EN Norms).Sand, fine size aggregates and large size aggregates are either round or crushed.

[0112] Mortars have been mixed using standard EN Mortar mixers and concrete samples have been mixed using conventional concrete mixers with capacity from 10 liters to 1 cubic meter.

[0113] Flow measurements were performed on cone test and standard spread metallic plate. Strength measurements on mortars were done on 4416 cm standard samples and concrete samples are tested on cubes (151515 cm) or cylinders (diam. 15 cm height 30 cm).

[0114] The self curing behavior or the shrinkage resistance was measured using cracking tests. The crack test carried out in the examples that follow was a modification of the norm ASTM C1579-2006 and is shown in table 3.

[0115] The crack test is an evaluation of the plastic shrinkage of mortar or concrete in severe conditions of curing: high temperature (about 40t) and dry environment (11-15% RH) and forced strong ventilation (about 5 m/sec).

[0116] The test was done by casting a concrete or a mortar in a 38 cm24 cm7 in a mould and placing the mould in a wood hot box (environmental chamber) for 24 hours. A stress riser, made of steel, with internal restraint was placed at the bottom of the mould.

[0117] Before placing the moulds in the hot box, a surface finishing has to be made, normally by a trowel or a metal straightedge.

[0118] In the hot box, two heating fans were used to produce a temperature of about 40 C. and a air speed of about 5 m/sec on the top surface of the moulds placed inside.

[0119] After 24 h from initial mixing, the area of the cracks that form on the surface was registered. The length and the width of the cracks were measured to calculate the area of the cracks. Instead of registering the area of the cracks, the minimum and maximum width of the central crack can be measured, which provides a range of the width appeared on the surface of the mortar/concrete.

[0120] Comparison of the modified crack test with the norm is shown in Table 3:

TABLE-US-00003 TABLE 3 description of the modified crack test used to characterize the resistance to shrinkage and the effect of the internal curing system. ASTM C1579 Modified crack test Use Fiber reinforced concrete (FRC) All types of mortar and concrete Dimension of the 2 times 56 35.5 10 cm 3 times 38 24 7 cm or test panels 1 time 77 44 7 cm Big stress height 6.35 cm 4.50 cm Hot box Monitor systems of evaporation rate, airflow, No monitor systems setting time Hot box for 2 panels test Hot box for 3 panels test Temperature 36 C. 42 C. Relative Humidity 30% 10% Wind velocity to have an evaporation rate of 1.0 Kg/m2 h 5-7 m/s Procedure Test stops at the final setting time and the Test stops at 24 h. panels test are stored until 24 h at 20 C. under plastic sheets. Results Cracking reduction ratio (CRR) at 24 h: Width range of cracking at (1 ((average crack width of FRC mix)/ 24 h (average crack width of control mix))) 100

[0121] The ring test is t is a modification of the standard ring test: ASTM C1581-04.

[0122] This method determines the age of cracking and induced tensile stress characteristics of mortar and concrete specimens under restrained shrinkage.

[0123] A sample of freshly mixed mortar or concrete is compacted in a circular mould around a steel ring. The restrained shrinkage behavior of concrete or mortar from the time of demoulding is monitored continuously by a system of strain gauges that measures the deformation of the material in time. Cracking of the test specimen is indicated by a sudden variation of the displacement value recorded by the strain gauges.

[0124] The age at cracking indicates the materials resistance to cracking under restrained shrinkage.

[0125] The test enables a measurement of the material deformation coupled with cracking behavior. The apparatus used I a steel mould consisting in a steel base, an inner steel ring and an outer ring (composed of 2 parts).

[0126] For mortar:

[0127] Mould: 16 mm thickness

[0128] Inner ring: 106 mm internal diameter; 130 mm external diameter; 67 mm height

[0129] Steel base: 82 mm internal diameter; 162 mm external diameter; 20 mm height

[0130] Outer ring: 162 mm internal diameter; 87 mm height

[0131] For concrete:

[0132] Mould: 40 mm thickness

[0133] Inner ring: 294.6 mm internal diameter; 320.1 mm external diameter; 165 mm height

[0134] Steel base: 400.1 mm internal diameter; 460 mm external diameter; 15 mm height

[0135] Outer ring: 400 mm internal diameter; 165 mm height

[0136] Procedure used: [0137] Oil the surface of the moulds and cast the material into them. [0138] At the time of demoulding, remove the two parts of the outer ring and the mould base from the concrete or mortar ring. [0139] Seal the bottom of the ring with paraffin wax or an adhesive aluminum foil tape. [0140] Place the ring in a flat support and glue the gauges (2-3). [0141] Seal the top with the same sealing agent use for the bottom. This operation allows having the drying of the material only from the external surface of the ring. [0142] Start the record of the gauges (one measurement every 5-30 minutes) [0143] A sudden decrease in the displacement measurement indicates cracking. The sudden decrease is usually about 10 microns of displacement for mortar specimen and about 2-6 microns of displacement for concrete specimen. [0144] The text is stopped at 28 days if no cracks were detected.

Comparative Example 1

[0145] A cementitious mix for concrete application was designed, using a superabsorbent polymer in powder as internal curing agent.

[0146] Four mixes were designed, including one referencewhere no SAP was used, therefore no internal formulated curing system was addedand three tests wherein three different concentrations of powdered SAP were adjoined.

[0147] The four mix designs are represented in table 4.

TABLE-US-00004 TABLE 4 Mix designs for Example 1, wherein the behavior of powdered SAP was observed MIX DESIGN Reference Test 1 Test 2 Test 3 OPC CEM I 52.5 R kg/m.sup.3 350 350 350 350 Water kg/m.sup.3 180 180 180 180 w/c 0.51 0.51 0.51 051 Paste Volume l/m.sup.3 291 291 291 291 Sand kg/m.sup.3 890 890 890 890 Coarse Aggregate kg/m.sup.3 390 390 390 390 (4.8 mm) Coarse Aggregate kg/m.sup.3 480 480 480 480 (8.16 mm) Superplasticizer % binder 0.59 0.59 0.59 059 kg/m.sup.3 2.07 2.07 2.07 2.07 Superabsorbent kg/m.sup.3 0.50 1.50 5.00 (Powder) RESULTS Slump Test mm 190 140 90 45 Slump Class S4 S3 S2 S2 Plastic shrinkage - Crack test crack YES YES YES NO crack width mm 1.8 1.6 0.8 Restrained shrinkage - Ring test Days for Cracking 3 5 8

[0148] As one can see from Table 4, SAPs are effective as internal curing agentswhile the Reference cementitious mix, in the crack test, experienced plastic shrinkage cracking, the cementitious mix 3, where 5 kg/m.sup.3 of SAP was added, had no cracks at the end of the crack test.

[0149] Also, the samples with SAP performed better in the Ring testwhile the Reference sample cracked just after 3 days, sample 3 had no cracking due to restrained shrinkage.

[0150] Despite the good and encouraging results obtained with the use of powder SAPs as internal curing agents, once the powdered SAP was introduced in the mix, it became stiff, having very reduced workability, due to the fast water uptake from the SAP and consequent swelling of the polymer. In fact, using the same mix design, the castable material produced went from a S4 to a S2 due to the water uptake by the superabsorbent. The possible solution of increasing the dosage of superplasticizer alters the characteristics of the material, hence undermining the quality of the final product, and therefore it should be avoided.

[0151] Despite the good results of using SAPs internal curing agents, the use of powdered material in real applications poses several constraints, namely due to reduced workability of the material after SAP addition.

Example 2

[0152] This example shows the procedure to formulate the internal curing system, according to one embodiment of the presently disclosed subject matter.

[0153] Water and a polysaccharide were mixed together in a vessel under continuous stirring. The mixing of the two ingredients continued for 2 hours, during the 2 hours the viscosity of the mix slightly increased. After the 2 hours, and still under continuous mixing, aluminium sulphate (Al.sub.2(SO.sub.4).sub.3) was added. Due to the ionic dissociation of the salt introduced, the viscosity of the mix suffered a sharp increase, reaching a peak close to 1200 MPa.Math.s. After this peak, the viscosity of the peak lowered, reaching about 200 MPa.Math.s. Around this time, more specifically 140 minutes after the beginning of the preparation of the formulation, a superabsorbent polymer was introduced in the mix.

[0154] The final mix had a milky consistency due to the polymer suspension, nevertheless no segregation or precipitation of the polymer was observed. The mix remained stable for 6 months.

[0155] The final mole percentages of the different components added during the formulation were included in the following ranges:

TABLE-US-00005 TABLE 5 Different ranges of the components used in the internal curing system formulation Water 60-70% Polysaccharide 0.1-0.5% Al.sub.2(SO.sub.4).sub.3 17-25% SAP 7-25% Total 100% For example: Water 60.00% Polysaccharide 0.10% Al.sub.2(SO.sub.4).sub.3 19% SAP 21% Total 100%

Example 3

[0156] The third example demonstrated the effect of different SAPs concentration in a concrete application.

[0157] The internal curing system dry solid content formulated in example 2 was used in this example in different percentages of binder: 0.3%, 0.6% and 1.1% (all dry solid contents, weight % with respect to the total binder content). Table 6 shows the different results obtained:

TABLE-US-00006 TABLE 6 Mix designs for a concrete application using 3 different concentrations of the internal curing system dry solid content of Example 2 MIX DESIGN Reference Test 1 Test 2 Test 3 OPC Cem I-52.5 kg/m.sup.3 300 300 300 300 Water kg/m.sup.3 165 165 165 165 w/c 0.55 0.55 0.55 0.55 Paste Volume l/m.sup.3 260 260 260 260 Sand kg/m.sup.3 870 870 870 870 Fine Aggregates kg/m.sup.3 480 480 480 480 Coarse Aggregates kg/m.sup.3 560 560 560 560 Superplasticizer % binder 0.7 0.7 0.7 0/ Internal Curing kg/m.sup.3 0.83 1.65 3.30 System % binder 0.3 0.6 1.1 Results: Slump mm 190 190 190 175 Slump Class S4 S4 S4 S4 Plastic shrinkage - Crack test crack YES YES YES NO crack width mm 0.35 0.45 0.25

[0158] Compared to the first example presented in the presently disclosed subject matter, the use of a formulated internal curing system didn't affect dramatically the slump of the concrete. The concrete remained a S4, even when 1.1% of dry solid content in the formulated internal curing system related to the binder content was added in the mix.

[0159] The crack test also revealed smaller cracks with the use of the formulated internal curing system. While in the reference sample, one had cracks with a maximum width of 0.35 mm, test 3 resulted in no cracks. Furthermore, the cracks obtained in test 2 had a smaller width than the one obtained in the reference test.

Example 4

[0160] In this example, one wanted to confirm the efficiency of the internal curing system formulated in example 2 in a concrete mix where other supplementary cementitious materials, in addition to Portland cement, were used, namely slag and lime filler. Again, different percentages of dry solid content of internal curing system were added, namely 0.3%, 0.5% and 1.1% related to the % of total binder used.

TABLE-US-00007 TABLE 7 Mix designs for example 4 MIX DESIGNS Reference Test 1 Test 2 Test 3 OPC Cem I 42.5 kg/m.sup.3 210 210 210 210 Slag kg/m.sup.3 90 90 90 90 Lime Filler kg/m.sup.3 10 10 10 10 Water kg/m.sup.3 161 161 161 161 w/b 0.52 0.52 0.52 0.52 Paste Volume l/m.sup.3 306 306 306 306 Sand kg/m.sup.3 860 860 860 860 Fine Aggregates kg/m.sup.3 475 475 475 475 Coarse Aggregates kg/m.sup.3 570 570 570 570 Superplasticizer % binder 0.7 0.7 0.7 0.7 Internal Curing kg/m.sup.3 0.825 1.65 3.3 System % binder 0.3 0.5 1.1 Results: Slump mm 200 210 190 190 Slump Class S4 S4 S4 S4 Plastic shrinkage - Crack test crack YES YES YES NO crack width mm 0.6 0.55 0.35 0

[0161] Once again, the slump of the final concrete was not significantly affected by the inclusion of the internal curing system formulated according to the presently disclosed subject matter.

[0162] After carrying on the crack test, one observed a reduction in the maximum crack width when higher dosage (in dry solid content) of formulated internal curing system was added; in fact, using 1.1% of formulated internal curing agent lead to no cracking of the material due to plastic shrinkage.

Example 5

[0163] Example 5 was carried out to investigate how the internal curing system of Example 2 would perform in screed applications.

[0164] The mix design for this test is detailed in Table 8.

TABLE-US-00008 TABLE 8 Mix design for screed application MIX DESIGN Blank Test Screed OPC CEM I 52.5 R kg/m.sup.3 517 517 Water kg/m.sup.3 256 256 w/c 0.50 0.50 Paste Volume l/m.sup.3 420 420 Sand 0/4 mm crushed kg/m.sup.3 695 695 Sand 0/4 mm round kg/m.sup.3 737 737 Superplasticizer % binder 0.7 0.7 kg/m.sup.3 3.41 3.41 Internal Curing System kg/m.sup.3 4.3 % binder 0.83 Results: Slump mm 260 255 Slump Class S5 S5 Plastic shrinkage - Crack test crack YES NO crack width mm 1.15

[0165] It is observed that the internal curing system is also effective in highly fluid mixes, such as for screed applications, maintaining the slump while reducing the plastic shrinkage cracking.

Example 6

[0166] The internal curing system of Example 2 was also tested in a very fluid mix designed to optimize the self-placing properties of the final product.

[0167] The mix design used and results obtained are compiled in Table 9.

TABLE-US-00009 TABLE 9 Mix design for fluid concrete MIX DESIGNS Reference Test 1 OPC Cement type II kg/m.sup.3 350 350 Aggregates 4/8 mm kg/m.sup.3 448 448 Aggregates 8/16 mm kg/m.sup.3 672 672 Sand 0/4 mm kg/m.sup.3 1120 1120 Water kg/m.sup.3 175 175 Superplasticiser % binder 0.8 0.8 Internal Curing System % binder 0.6 kg/m.sup.3 2.1 RESULTS Fresh properties Slump flow mm 550 620 Slump Class SF1 SF1 Restrained shrinkage - Ring test time of crack h 171 >250 Compressive strength 28 days Mpa 63.78 62.86

[0168] One can see that the slump was not influenced by the addition of the internal curing system used while the time of cracking in the Ring test was much higher when the internal curing system was used (more than 250 hours to crack, compared to the reference that took only 171 hours).

Example 7

[0169] To understand how the formulation would affect a concrete mix design having a high content of binder, example 7 was carried out using a total of 436 l/m.sup.3 of paste volume, including 400 kg/m.sup.3 of Cement type II and 185 kg/m.sup.3 of fly ash. The amount of dry solid content of the internal curing system was increased to 2% of weight of binder.

TABLE-US-00010 TABLE 10 Mix design and results obtained for Example 7 MIX DESIGNS Reference Test 1 OPC Cement type II kg/m.sup.3 400 400 Fly Ash kg/m.sup.3 185 185 Aggregates 4/8 mm kg/m.sup.3 294 294 Aggregates 8/16 mm kg/m.sup.3 515 515 Sand 0/4 mm kg/m.sup.3 659 659 Water kg/m.sup.3 215 215 Paste Volume l/m.sup.3 436 436 Superplasticiser (ASC) % binder 0.9 0.9 Internal Curing System (ASC) % binder 2 kg/m.sup.3 11.7 RESULTS Fresh properties Slump flow mm 720 725 Slump Class SF2 SF2 Restrained shrinkage - Ring test time of crack h 48 >672 Compressive strength 28 days Mpa 65.7 64.1

[0170] One can see that the slump is not affected by the use of the internal curing system. Also, the Ring Test results are better when the internal curing system formulation is addedafter 28 days the concrete had not cracked when the internal curing system was used, while when no internal curing system was added, the concrete cracked after 48 hours.