LIGHTWEIGHT CONCRETE

Abstract

A lightweight structural concrete formulation comprises a wet mix of about 460 kg/m.sup.3 of cementitious material such as ordinary Portland cement of which about 50 percent has been replaced by ground granulated basic furnace slag (GGBFS) and 7 percent by silica fume (SF) in other words the mix introduces between about 178 and 228 kg/m.sup.3 therefore the combination is good to produce secondary reaction products when the cement hydrates which produces secondary calcium silicate hydrate (C-S-H) which makes the structure dense and thereby increases its mechanical durability characteristics of the concrete product. Possible ratios of GGBFS and SF are 30-70 percent and 5-10 percent, respectively. By making the structures dense increases the mechanical and durability characteristics of the concrete product. Other ratios have been made including GGBFS of 30-70 percent and silica fume 5-10 percent, respectively. It can be noted that the silica fume was added to the mixture as a supplementary cementitious material (SCM) not as an aggregate. It should also be noted that the particle sizes of GGBFS ranges between about 20-40 mm and that of silica fume is less than 20 mm.

Claims

1. A lightweight structural concrete comprising and/or consisting of (made from) a wet concrete mix of Portland cement (OPC) 198 kg/m.sup.3, GGBFS 232 kg/m.sup.3, silica fume (SF) about 32 kg/m.sup.3, perlite aggregate 140 kg/m.sup.3, water in an amount of water/cement of about 0.25 and minor amounts of coarse aggregate and fine aggregate.

2. A lightweight structural concrete product according to claim 1, in which said wet mix comprises between about 178 and 228 kg/m.sup.3 OPC, between about 207 and 253 kg/m.sup.3 GGBFS, between about 29 and 35 kg/m.sup.3 silica fume, between about 100 and 176 kg/m.sup.3 of perlite aggregates and minor amounts of coarse fine aggregate.

3. A lightweight structural concrete product according to claim 2, in which said light aggregates are present in amount of between about 110 and 160 kg/m.sup.3 for a lightweight structural concrete product.

4. A lightweight structural concrete product according to claim 3, in which said perlite aggregate comprises about 112 kg/m.sup.3 per unit of cement.

5. A lightweight structural concrete product according to claim 4, in which said perlite aggregate comprises about 140 kg/m.sup.3 per unit of cement.

6. A lightweight structural concrete product according to claim 4, in which said perlite aggregate comprises about 160 kg/m.sup.3 per unit of cement.

7. A lightweight structural concrete product made from a wet mix consisting of about 178 and 228 kg/m.sup.3 of ordinary Portland cement; between about 207 and 253 kg/m.sup.3 GGBFS; between about 29 and 35 kg/m.sup.3 per unit of cement of silica fume; and about 176 kg/m.sup.3 per unit of cement.

Description

DESCRIPTION OF THE DRAWINGS

[0014] FIG. 1 is a photograph of the molded cubical specimens of various concrete mixtures;

[0015] FIG. 2 is a photograph of molded cylindrical specimens of the concrete mixtures;

[0016] FIG. 3 is a photograph of de-molded concrete specimens;

[0017] FIG. 4 is a photograph of the compressive testing machine used in evaluating the mixtures in accordance with the present invention;

[0018] FIG. 5 is a graphical illustration of the unit weight in the different concrete mixtures prepared with perlite aggregate;

[0019] FIG. 6 is a graphical illustration of a comparison of compressive strength in the concrete specimens prepared with perlite aggregate;

[0020] FIG. 7 is a graphical illustration of the compressive strength in MPa versus evolution of compressive strength in the concrete specimens prepared with and without perlite aggregate;

[0021] FIG. 8 is a graphical illustration of water absorption in the different concrete mixtures prepared with and without perlite aggregate;

[0022] FIG. 9 is a photograph of the laboratory set-up for permeability testing;

[0023] FIG. 10 is a graphical illustration of chloride permeability in the concrete specimens prepared by incorporating perlite aggregate;

[0024] FIG. 11 is a photograph of the data acquisition system used to measure drying shrinkage;

[0025] FIG. 12 is a graphical illustration showing the drying shrinkage strains of various concrete mixes; and

[0026] FIG. 13 is a graphical illustration of the thermal resistance of concrete specimens prepared with varying quantities of perlite aggregate.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

[0027] An initial embodiment of the invention is directed to a lightweight structural concrete comprising (made from) a wet mix of ordinary Portland cement (OPC) about 178 to about 228 kg/m.sup.3; GGBFS between about 207 and 253 kg/m.sup.3; between about 29 and 35 kg/m.sup.3 Silica Fume (SF); between about 100 and 176 kg/m.sup.3 perlite aggregate, plus minor amounts of coarse and fine aggregates plus 0.5 percent of a polycarboxylate superplasticizer.

[0028] A second embodiment of the invention includes between about 482 and 1218 kg/m.sup.3 coarse aggregate and between about 160 and 655 kg/m.sup.3 fine aggregates.

[0029] Preparation and Testing of Concrete Specimens

[0030] The concrete specimens for the four concrete mixes were tested according to the ASTM standards at different curing periods to evaluate the mechanical and durability properties as per the schedule of curing. FIGS. 1 and 2 shows the cube and cylindrical specimens being prepared for concrete mixtures, respectively. FIG. 3 illustrates de-molded specimens ready to start curing. The tests conducted and frequency together with the sample sizes is shown in Table 2.

TABLE-US-00002 TABLE 2 Specimen sizes for different test conducted. Task Specimen size, mm Testing ages Unit Weight as per ASTM C138 100 100 cube One day Evolution of Compressive Strength fc 100 100 cube 1, 3, 7, 14, 28 and 90 as per ASTM C39 Evaluation of shrinkage as per ASTM C 50 50 250 prism Periodic monitoring 157 after 28 days of curing Chloride permeability as per ASTM 100 200 cylinder 28 and 90 days of C1202 curing Water absorption as per ASTM C642 75 150 cylinder 28 and 90 days of curing Reinforcement Corrosion as per ASTM 75 150 cylinder Periodic monitoring C876 after 28 days of curing Thermal conductivity 350 350 50 slab 14 days of curing

[0031] Results and Discussion

[0032] Unit Weight and Compressive Strength

[0033] Unit weight of concrete was measured after demolding the concrete specimens after one day of casting before being cured by immersing in potable water. Digital compressive strength testing machine as shown in FIG. 4 was used to determine the strength of different concrete mixtures. The unit weights of developed concrete mixes are shown in FIG. 5. FIG. 6 shows the comparison of compressive strength with time in the four concrete mixtures cured under water for three months. Additionally, the compressive strength results are also illustrated in a line plot as depicted in FIG. 7. Unit weight was in the range of 1700 kg/m.sup.3 to 2500 kg/m.sup.3, the lowest being in the 20% perlite aggregate concrete (M20), while, highest for the concrete without perlite aggregate (M0). There was a reduction in unit weight from 20% to 30% in the various mixtures of concrete containing perlite aggregate as compared to the one having no lightweight aggregate.

[0034] The compressive strength increased with curing period in all the concrete mixtures. 28 days compressive strength in the concrete mixes containing, 10%, 15% and 20% perlite aggregate was 41.6 MPa. 31.1 MPa and 23.7 MPa, respectively. However, compressive strength of concrete without perlite aggregate after 28 days of curing was 62.5 MPa. There was a marginal increase in the compressive strength in the concrete mixtures when curing extended up to 90 days. At the end of 90 days curing compressive strength was 49.2 MPa, 33.0 MPa and 26.1 MPa, respectively, for mixtures containing 10%, 15% and 20% perlite aggregate. The developed concrete mixtures, particularly prepared with 10% and 15% perlite aggregate, can be utilized as structural concrete as the compressive strength is more than 30 MPa. Moreover, concrete mixture prepared with 10% perlite aggregate developed compressive strength of the order 49.2 MPa at the end of 90 days curing in which there was 20% reduction in unit weight as compared to concrete mixture containing no perlite aggregate.

[0035] Water Absorption

[0036] In order to determine the water absorption of the concrete mixtures after completing a specified number of days of curing, cylindrical specimens were dried at 110 C. in the oven approximately 24 hours until attaining a constant weight, subsequently the specimens were saturated in the water for about 48 hours. Resulting water absorption is calculated in terms of percentage and demonstrated in the FIG. 8 for different concrete mixtures prepared with and without perlite aggregate.

[0037] The results show that the water absorption was in the range of 1.31% to 7.12% and 1.44% and 6.50%, in the concrete specimens cured for 28 and 90 days of curing, respectively. Water absorption reduced marginally when the curing extended from 28 days to 90 days. Perlite aggregate concrete performed well, particularly at 10% and 15% replacement levels, according to water absorption results as the values are comparable to OPC concrete used in the field.

[0038] Chloride Permeability

[0039] FIG. 9 shows a set-up used to determine chloride permeability, a key durability parameter. The chloride permeability in the concrete mixes M0, M10, M15 and M20 prepared with 0%, 10%, 15% and 20% perlite aggregate, respectively, after 28 and 90 days of curing is depicted in FIG. 10. As expected, the chloride permeability decreased with curing age in all the concrete specimens. Chloride permeability is highest in concrete specimens for mix M20 and lowest for mix M0 after 28 and 90 days of curing. In the concrete mix, prepared with a 20% perlite aggregate, chloride permeability is greatly reduced when the curing extended from 28 days to 90 days.

[0040] For specimens cured for 28 days, chloride permeability in the mixes M0, M10, M15 and M20 are 216, 354, 408 and 844 coulombs respectively. After 90 days of curing, the chloride permeability of mixes M0, M10, M15 and M20 decreases to 130, 228, 258 and 265 coulombs, respectively. Table 3 shows the ASTM C1202 classification of concrete quality based on permeability. The chloride permeability in the concrete mixtures prepared with and without perlite aggregate at all curing periods, fall into Very Low category as per ASTM C 1202. These results indicate very low penetrability of chloride in all the concrete mixtures.

TABLE-US-00003 TABLE 3 ASTM C1202 chloride permeability classification. Charge Passed, Coulombs Penetrability >4000 High 2000-4000 Moderate 1000-2000 Low 100-1000 Very Low <100 Negligible

[0041] Drying Shrinkage

[0042] FIG. 11 illustrates the data acquisition system used to measure drying shrinkage strain with the help of linear variable differential transducer (LVDT). The drying shrinkage strain in the concrete specimens is depicted in FIG. 12. The drying shrinkage strain increased with time in all the concrete specimens. Also, it increased with increasing perlite aggregate content. According to the data available to date (28 days) the drying shrinkage strain in all concrete mixes is less than 700 microns. The drying shrinkage strains recorded in the concrete mixtures M0, M10, M15 and M20 are 650, 585, 550 and 497 microns, respectively.

[0043] Thermal Resistance

[0044] The thermal performance of the concrete mixtures prepared with and without perlite aggregate was determined by using 35 cm35 cm5 cm slab specimen. Thermal resistance of all the concrete mixtures prepared in the study is demonstrated in FIG. 13. Thermal resistance increased with increasing the perlite aggregate content. The highest resistance of 0.510 m.sup.2 K/W was measured in the concrete mix, prepared with a 20% perlite aggregate, while, it was 0.202 m.sup.2K/W in the mixture without perlite aggregate. Therefore, there was more than two and half times more thermal resistance in the 20% perlite aggregate concrete as compared to the mixture containing no perlite aggregate.

CONCLUSIONS

[0045] The data developed in this study indicate that there was 20 to 30% reduction in the weight of concrete in the mixes prepared by incorporating perlite aggregate. The developed concrete mixtures can be potentially used for structural purposes as the compressive strength is more than 30 MPa, particularly for the concrete mixtures prepared with 10 and 15% perlite aggregate. Durability performance of the concrete mixtures prepared in the study was satisfactory as the water absorption and chloride permeability of the developed concrete was reasonably low. The chloride permeability, a key durability parameter, in the concrete mixtures prepared with and without perlite aggregate at all curing periods, fall into Very Low category as per ASTM C 1202. These results indicate very low penetrability of chloride in all the concrete mixtures. According to the data available to date, drying shrinkage strain in the concrete mixtures is comparable to OPC concrete used in the field. Another important aspect of the study is that the thermal resistance of the developed concrete mixtures utilizing perlite aggregate is high as compared to the mix containing no perlite aggregate. There was more than two and half times more resistance in the concrete mixture containing 20% perlite aggregate as compared to the control mix. Therefore, according to the results of this endeavor, developed light weight durable concrete mixtures could be potentially useful in structural elements with high thermal resistance.

[0046] Advantages of the Developed Product

[0047] Following are the advantages of the developed concrete mixtures: [0048] i. Developed concrete mixtures are 20 to 30% lighter than the conventional concrete. [0049] ii. Due to the fact that the compressive strength of developed concrete is more than 30 MPa, could be potentially utilized for structural purposes. Moreover, the concrete mixture containing 10% perlite aggregate after 90 days of curing developed strength close to 50.0 MPa, which is quite high. [0050] iii. Enhanced service-life of concrete structures as the key durability parameters of the developed concrete are excellent as compared to the other lightweight concretes being used in the construction industry. [0051] iv. Reduction in the quantity of cement, as a result of partially replacing it with industrial byproducts, leading to a decrease in the carbon footprint of the construction industry. [0052] v. The added advantage of the developed concrete mixtures is that, their thermal resistance is high which will result in energy saving of buildings.

[0053] Limitations

[0054] There are no limitations on the use of the developed concrete mixtures, as long as the silica fume and GGBFS that are used in their preparation meet the relevant specifications (ASTM C1240 for silica fume and ASTM C989 for Blast Furnace Slag).

[0055] While the invention has been defined in accordance with its preferred embodiments, it should be recognized that changes and modifications may be made therein without departing from the scope of the appended claims.