CONCRETE PAVING BLOCKS WITH HIGH STRENGTH AND LOW EFFLORESCENCE

Abstract

Efflorescence resistance of concrete blocks is enhanced through the use of glass powder in the concrete composition. The glass powder permits a reduction in the cement content; the glass powder also creates a pozzolanic reaction to change the free calcium ions in calcium hydroxide to calcium silicate to fix the calcium ions inside concrete. The composition includes cementitious binding material of ordinary Portland cement, fly ash, calcium sulfoaluminate cement, ground-granulated blast-furnace slag in an amount from 20 to 25 wt. %. Coarse aggregate is provided from 10 to 15 wt. percent. Fine aggregate is from 32 to 39 wt. %. The composition further includes glass powder having a diameter of less than approximately 75 microns in an amount from 17 to 23 wt. %. Water is present in an amount from 6 to 9 wt. %. The dry density of formed paving blocks is 1800-2200 kg/m.sup.3.

Claims

1. An efflorescence-resistant concrete paving block composition comprising: a cementitious binding material selected from one or more of ordinary Portland cement (OPC), fly ash (FA), calcium sulfoaluminate cement (CSA), ground-granulated blast-furnace slag (GGBS), metakaolin (MK), or silica fume (SF); coarse aggregate, wherein at least 90 percent of the coarse aggregate has a diameter of less than approximately 10 mm; fine aggregate having a diameter of approximately 0.75 to 4.75 mm; glass powder having a diameter of less than approximately 75 microns; water; and plasticizer; wherein a ratio of water to cementitious binder material is 0.2 to 0.5 by weight; a ratio of coarse plus fine aggregate to cementitious binder material is 2 to 6 by weight; a ratio of fine aggregates to coarse aggregates is 2 to 5 by weight; and a dry density of formed paving blocks from the composition is 1800-2200 kg/m.sup.3.

2. The composition of claim 1, wherein the fine aggregates have 40-50% of a particle size within the range of 1.18-2.36 mm and 30-40% of a particle size within the range of 0.3-0.6 mm.

3. The composition of claim 1, wherein the binder includes a mixture of ordinary Portland cement (OPC) and fly ash (FA).

4. The composition of claim 1, wherein the glass powder is recycled glass powder.

5. The composition of claim 1, wherein a ratio of water to cementitious binder material is 0.3 to 0.35 by weight.

6. An efflorescence-resistant concrete paving block formed from the composition of claim 1.

7. An efflorescence-resistant concrete paving block composition comprising: a cementitious binding material selected from one or more of ordinary Portland cement (OPC), fly ash, calcium sulfoaluminate cement (CSA), ground-granulated blast-furnace slag (GGBS) in an amount from 20 to 25 wt. %; coarse aggregate having a diameter less than approximately 10 mm in an amount from 10 to wt. percent; fine aggregate having a diameter of approximately 0.75 to 4.75 mm in an amount from 32 to wt. %; glass powder having a diameter of less than approximately 75 microns in an amount from 17 to 23 wt. %; water in an amount from 6 to 9 wt. %; and plasticizer; wherein the dry density of paving blocks formed from the composition is 1800-2200 kg/m.sup.3.

8. The composition of claim 7, wherein the fine aggregates have 40-50% of a particle size within the range of 1.18-2.36 mm and 30-40% of a particle size within the range of 0.3-0.6 mm.

9. The composition of claim 7, wherein the binder includes a mixture of ordinary Portland cement (OPC) and fly ash (FA).

10. The composition of claim 7, wherein the glass powder is recycled glass powder.

11. The composition of claim 7, wherein a ratio of water to cementitious binder material is 0.3 to 0.35 by weight.

12. An efflorescence-resistant concrete paving block formed from the composition of claim 7.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] FIG. 1 is a plot of the compressive strength vs. the water to cement ratio.

[0011] FIG. 2 is a plot of compressive strength vs. the aggregate to cement ratio.

[0012] FIG. 3 is a plot of compressive strength vs. the fine to coarse aggregate ratio.

[0013] FIG. 4 is a plot of compressive strength vs. glass content.

[0014] FIG. 5 is a plot of the gradation of fine aggregate.

[0015] FIG. 6 is a plot of the 10 mm aggregate.

[0016] FIG. 7 is a scatter plot of 28 days' compressive strength.

[0017] FIG. 8 is a photograph of two samples that have undergone efflorescence testing.

[0018] FIG. 9 shows the conductivity of the fly ash group.

[0019] FIG. 10 shows the conductivity of the glass powder group.

DETAILED DESCRIPTION

[0020] Masonry and cement-based materials which contain high alkali content are susceptible to efflorescence since soluble salts during hydration are inevitable in the concrete-forming process. To mitigate the efflorescence of concrete paving blocks, the present invention determines an appropriate cement content, water to cement ratio, and permeability. Additionally, as the major source of calcium ion of free Ca(OH).sub.2 is generated from the hydration of cement, the invention provides a mechanism whereby Ca(OH).sub.2 produced by cement can be consumed by a pozzolanic reaction. For the water to cement ratio, minimizing the water to cement ratio can decrease the medium (water) that brings soluble ions to the surface to react with CO.sub.2 in the air. Further, a good gradation of the aggregate can enhance the permeability, reducing the pores for soluble salt migration.

[0021] In particular, it was determined that the use of glass powder in the concrete composition permits a reduction in the cement content while the glass powder reacts to change the free calcium ions in calcium hydroxide to calcium silicate to fix the calcium ions inside the concrete. This prevents the reaction between calcium hydroxide and carbon dioxide in the air that creates the efflorescence.

[0022] Various ratios among different concrete constituents were determined to create an appropriate balance between strength, cost, and efflorescence reduction. In particular, the invention determined the appropriate water to cement ratio, aggregate to cement ratio, fine to coarse aggregate ratio, and glass content.

[0023] The resultant composition forms a low efflorescence concrete block. As used herein, the expression “low efflorescence” means that the developed formula caused lower efflorescence than existing plant formulas through conductivity tests and water absorption tests, the conductivity test value can be reduced more than 20% of the existing plant formulas, and water absorption can be reduced to 2.5%, compared with the existing plant formula (3.91%).

[0024] Water-to-Cement Ratio

[0025] Water is necessary for cement hydration; that is, to complete the chemical reactions necessary to form a strong cement product. The aggregate strength, interfacial bonding strength, and the strength of the cement matrix contributes to the compressive strength of the concrete block formed from the composition. The water-to-cement ratio mainly has an impact on the strength of the cement matrix. Excess water causes strength reduction, drying shrinkage, and loss of abrasive resistance. Low water-to-cement ratio causes insufficient hydration and low workability. Thus, there is an optimal water-to-cement ratio which makes a full coating on the surface of aggregates.

[0026] The present invention examined five formulas with water-to-cement ratios of 0.2, 0.25, 0.3, 0.35 and 0.4. 7-day compressive strength was used as an index. According to previous tests, the compressive strength has a relation to the dry density presented by the linear regression equation Y=0.1628X−297.08. The samples have density variations. To eliminate the impact caused by density variations, the present invention transfers the real compressive strength to the compressive strength at a fixed dry density of 2150 kg/m.sup.3 by the formula:

P.sub.c=P.sub.o+0.1628×(2150−ρ.sub.o)

[0027] P.sub.c: Converted compressive strength

[0028] P.sub.o: Real compressive strength

[0029] ρ.sub.o: Real dry density

[0030] Table 1 depicts the water-to-cement ratio for different compositions to determine water-to-cement ratios for use in the compositions of the present invention.

TABLE-US-00001 TABLE 1 Water-to-Cement Ratio Corrected Aggregate 7 Days 7 days Fine aggregate Coarse Admixture Dry compressive compressive W/C Binder Coarse aggregate Water density strength strength ratio OPC SCM Glass sand 10 mm Water reducer (kg/m3) (MPa) (MPa) 0.20 912.7 520.7 1563.3 561.7 182.5 2.8 2121.1 23.2 27.94 0.25 912.7 520.7 1563.3 561.7 228.2 2.8 2169.1 31.0 27.86 0.30 912.7 520.7 1563.3 561.7 273.8 2.8 2177.9 45.8 41.26 0.35 912.7 520.7 1563.3 561.7 319.5 2.8 2149.0 40.9 41.01 0.40 912.7 520.7 1563.3 561.7 365.1 2.8 2199.8 44.1 35.98

[0031] A curve of the compressive strength-water to cement ratio is depicted in FIG. 1. When water-to-cement ratio is low, the fluidity is low. The aggregate is not fully coated. Increased water-to-cement ratio enhances the bonding strength. When the water-to-cement ratio is high, the aggregate is fully coated. However, excess water reduces the strength of the cement matrix.

[0032] For the compositions tested in FIG. 1, the highest strength water-to-cement ratio was determined to be 0.32.

[0033] 2. Aggregate-to-Cement Ratio Vs Compressive Strength

[0034] Compressive strength is related to both aggregate strength and to the strength of the cement matrix. Aggregates and cement are the main components of solid concrete. To determine the optimum aggregate-to-cement ratio, the total amount of solids remained unchanged while adjusting the amount of cement. Generally, compressive strength increases with increasing cement content. However, excess cement may cause low fluidity as cement consumes most of the water. Table 2 shows the six tested compositions with aggregate-to-cement ratios of 1.5, 2.0, 2.5, 3.0, 3.5 and 4.0.

TABLE-US-00002 TABLE 2 Aggregate to cement ratio: Corrected Aggregate (g) Admixture 7 Days 7 days Fine aggregate Coarse (g) Dry compressive compressive A/C Binder (g) Coarse aggregate Water Water density strength strength ratio OPC SCM Glass sand 10 mm (g) reducer (kg/m3) (MPa) (MPa) 1.5 1423.39 420.22 1261.6 453.27 228.18 2.81 2164.1 50.01 48.72 2.0 1186.16 466.91 1401.78 503.63 228.18 2.81 2162.8 51.03 48.94 2.5 1016.71 500.26 1501.90 539.61 228.18 2.81 2126.7 40.57 44.35 3.0 889.62 525.27 1577 566.59 228.18 2.81 2170.0 31.10 27.85 3.5 790.77 544.73 1635.41 587.57 228.18 2.81 2130.2 25.00 28.22 4.0 711.70 560.29 1682.13 604.36 228.18 2.81 2101.7 19.19 27.05

[0035] The compressive strength decreases as the aggregate-to-cement ratio increases which complies with the prediction. The R-squared value is 0.8436 which indicates a strong relationship. It is noted that the compressive strength varies little when the aggregate-to-cement ratio is larger than 3 as seen in FIG. 2.

[0036] 3. Fine-to-Coarse Aggregate Ratio Vs. Compressive Strength

[0037] Coarse aggregates have a large area to volume ratio. It is more effective for the binder to connect coarse aggregates. Fine aggregates fill in the voids between coarse aggregates and enhance the interlock strength of the concrete. Table 3 shows five tested compositions to determine the optimum fine-to-coarse aggregate ratio vs. the compressive strength of the concrete. FIG. 3 shows that the optimum fine-to-coarse aggregate ratio for the tested compositions for compressive strength is 4.5. Compressive strength with the fine/coarse ratio in the range from 4.0 to 5.0 fluctuates slightly.

TABLE-US-00003 TABLE 3 Fine to coarse aggregate ratio Corrected Aggregate (g) Admixture 7 Days 7 days Fine aggregate Coarse (g) Dry compressive compressive F/C Binder (g) Coarse aggregate Water Water density strength strength ratio OPC SCM Glass sand 10 mm (g) reducer (kg/m3) (MPa) (MPa) 3.5 865 489.3 1467.8 637.9 259.5 2.8 2127.6 40.98 37.30 4.0 865 505.3 1515.7 574.0 259.5 2.8 2164.1 41.73 39.40 4.5 865 518.3 1554.7 522.0 259.5 2.8 2182.6 46.00 40.52 5.0 865 529.3 1587.7 478.0 259.5 2.8 2172.2 43.58 39.80 5.5 865 538.4 1615.0 441.6 259.5 2.8 2163.1 40.08 37.90

[0038] 4. Glass Content Vs. Compressive Strength

[0039] Glass sand has a similar gradation to fine aggregate. It contains ultra-fine glass (<100 μm) which improves the compressive strength. Further, it optimizes the gradation of aggregates. However, the strength of glass is lower than that of aggregates; glass is also brittle. To identify an optimum glass content, five compositions were selected with different glass contents. Glass content is defined as:

[00001]$\mathrm{Glass}\mathrm{content}=\frac{\mathrm{Glass}}{\mathrm{Glass}+\mathrm{Coarse}\mathrm{sand}}\mathrm{by}\mathrm{mass}.$

[0040] The compressive strength reaches a peak value when the glass content is 0.3 as seen in FIG. 4. After that, it decreases slowly. By observing the appearance of samples, potholes increase on the surface with an increase in the glass content. Therefore, 0.35 was used as an optimum glass content which can both increase compressive strength and consume glass without defects on the surface.

TABLE-US-00004 TABLE 4 Glass content Corrected Aggregate (g) Admixture 7 Days 7 days Fine aggregate Coarse (g) Dry compressive compressive Glass Binder (g) Coarse aggregate Water Water density strength strength Content OPC SCM Glass sand 10 mm (g) reducer (kg/m3) (MPa) (MPa) 0.1 889.6 210.2 1892.0 566.6 266.9 2.8 2177.9 38.94 34.20 0.2 889.6 420.5 1681.8 566.6 266.9 2.8 2196.6 47.10 39.20 0.3 889.6 630.7 1471.6 566.6 266.9 2.8 2165.1 46.18 43.60 0.4 889.6 840.9 1261.4 566.6 266.9 2.8 2191.9 49.29 42.20 0.5 889.6 1051.1 1051.2 566.6 266.9 2.8 2181.9 48.27 42.90

[0041] Based on the above, a composition for a low efflorescence, high strength paving block includes a cementitious binding material of ordinary Portland cement (OPC), fly ash, calcium sulfoaluminate cement (CSA), ground-granulated blast-furnace slag (GGBS) or mixtures thereof. The composition further includes coarse aggregate; at least 90 percent of the coarse aggregate has a diameter of less than approximately 10 mm. Fine aggregate is provided having a diameter less than approximately 0.75 to 4.75 mm. The composition also includes glass powder having a diameter of less than approximately 75 microns along with water and an optional superplasticizer. In the composition, a ratio of water to cementitious binder material is 0.2 to 0.5 by weight. A ratio of coarse plus fine aggregate to the cementitious binder material is 2 to 6 by weight. The ratio of fine aggregates to coarse aggregates is 2 to 5 by weight and the dry density of formed paving blocks is 1800-2200 kg/m.sup.3.

[0042] The composition may optionally include a variety of recycled components. For example, recycled fine aggregate may be used (for example, stone fines) as well as recycled coarse aggregate (for example, recycled concrete aggregate). Glass components may also optionally include recycled glass.

[0043] In another aspect, the present invention provides an efflorescence-resistant concrete paving block composition having a cementitious binding material of ordinary Portland cement (OPC), fly ash, calcium sulfoaluminate cement (CSA), ground-granulated blast-furnace slag (GGBS) in an amount from 20 to 25 wt. %. Coarse aggregate is provided having a diameter less than approximately 10 mm in an amount from 10 to 15 wt. percent. Fine aggregate is provided having a diameter less than approximately 3 mm in an amount from 32 to 39 wt. %. The composition further includes glass powder having a diameter of less than approximately 75 microns in an amount from 17 to 23 (19.9 being an optimum value) wt. %. Water is present in an amount from 6 to 9 wt. %; and the dry density of formed paving blocks is 1800-2200 kg/m.sup.3.

Examples

[0044] The examples relate to determination of low efflorescence compositions using glass powders. The raw materials were analyzed. The 10 mm aggregate contains around 10% fine aggregate which is taken into consideration when calculating the fine to coarse aggregate ratio which is to say:

[00002]$\mathrm{Fine}\mathrm{to}\mathrm{coarse}\mathrm{aggregate}\mathrm{ratio}=\frac{M_{\mathrm{Glass}}+M_{\mathrm{Sand}}+10\%M_{10\mathrm{mm}}}{90\%M_{10\mathrm{mm}}}$

[0045] FIG. 5 shows the fine aggregate grading curve. FIG. 6 shows the 10 mm aggregate curve.

[0046] Moisture content of solid starting ingredients has an impact on the selection of a particular water-to-cement ratio. In the plant, an operator can measure the water content after mixing. The water-to-cement ratio is used as an index. The moisture in the solid increases the actual water-to-cement ratio.

[0047] Recycled glass contains almost no moisture. For the coarse sand and 10 mm aggregate, the following steps are applied to measure the moisture content:

[0048] Weigh the sample and put it in the oven.

[0049] After 24 hrs, take out the sample and weigh it.

[0050] Compare the mass difference and calculate the moisture content.

[00003]$\mathrm{Moisture}\mathrm{content}=\frac{\mathrm{Mass}\mathrm{after}\mathrm{drying}-\mathrm{Mass}\mathrm{before}\mathrm{drying}}{\mathrm{Mass}\mathrm{before}\mathrm{drying}}$

[0051] The moisture content of coarse sand is 4.17% while the moisture content of 10 mm aggregate is 1.01%. Therefore, drying oven was used to remove the moisture content of the coarse sand and 10 mm aggregate before mixing.

[0052] Sample Preparation

[0053] Two methods are used for the preparation of samples. One is to compact material on a vibration table. By controlling the vibration and loading, the height and density are within an accepted range.

[0054] The other is to compact material without vibration. The examples use the second method. Without vibration, a very high-density sample may not be obtained.

[0055] Compressive Strength Test

[0056] An advanced test machine is used to test the compressive strength in the axial direction. The loading rate is set as 15 kN/s. Before compressive strength test, mass and height are measured to calculate the dry density.

[0057] Dry Density Vs Compressive Strength

[0058] Three batches of 80 mm paving blocks (each batch contains 54 pieces) were analyzed. The average 28-day compressive strength is 69.04 MPa. The maximum 28-day compressive strength is 88.03 MPa. The minimum 28-day compressive strength is 50.4 MPa. Linear regression was used to analyze the relationship between the 28-day compressive strength and the dry density, plotted in FIG. 7. The linear regression equation is Y=0.1628X−297.08. The R-squared value is 0.7753 which is larger than 0.7. Therefore, the dry density is deemed to have a strong correlation to the 28-day compressive strength. Based on the regression equation, the expected dry density should be no less than 2100 kg/m.sup.3 to achieve a 45 MPa compressive strength. Considering the variation during commercial production, 2150 kg/m.sup.3 was selected as the minimum dry density.

[0059] It is noticeable that mass loss occurs after mixing. For example, the weighted mixture may fall out when filling it into the mold. Water evaporation happens during the curing. To predict the accurate value of the dry density, a relationship is built between wet density and dry density. A group of samples was prepared to determine the mass loss rate which is defined as:

[00004]$\mathrm{Mass}\mathrm{loss}\mathrm{rate}=\frac{\mathrm{Wet}\mathrm{mass}-\mathrm{Dry}\mathrm{mass}}{\mathrm{Wet}\mathrm{mass}}\mathrm{Wet}\mathrm{mass}:\mathrm{mass}\mathrm{of}\mathrm{the}\mathrm{mixture}\mathrm{before}\mathrm{filling}\mathrm{the}\mathrm{material}\mathrm{Dry}\mathrm{mass}:\mathrm{mass}\mathrm{of}\mathrm{the}\mathrm{paving}\mathrm{blocks}\mathrm{after}\mathrm{curing}$

[0060] After erasing the inaccurate data of Sample 4 and Sample 7, the average mass rate is 2.30%. The designed wet density should be no less than 2200 kg/m.sup.3.

TABLE-US-00005 TABLE 5 Mass loss rate Average Wet Dry Mass Mass mass loss mass (g) mass(g) loss (g) loss rate rate 1 3600 3526.4 73.6 2.04% 2.30% 2 3400 3324.7 75.3 2.21% 3 3500 3411.5 88.5 2.53% 4 3450 3328.8 121.2 5 3550 3465.7 84.3 2.37% 6 3550 3466.4 83.6 2.35% 7 3550 3416.3 133.7

[0061] Optimum Formula Design

[0062] Considering the above factors, a particular optimum formula was determined in Table 6

TABLE-US-00006 TABLE 6 Optimum formula Aggregate (g) Admixture Fine aggregate Coarse (g) Dry Binder (g) Coarse aggregate Water Water density OPC SCM Glass sand 10 mm (g) reducer (kg/m.sup.3) Optimum 832.7 715.3 1328.6 454.3 266.4 2.6 2150

[0063] The above formula is based on considerations of highest compressive strength. However, from an environmental and cost standpoint, it is also a target to save 15% Portland cement. Increasing A/C ratio and reducing dry density are two primary methods for cement saving. Based on the optimum formula, six formulas were selected in the lab for performing a compressive strength test. The height should be 80±2 mm and the 28-day compressive strength should be higher than 45 MPa. Generally, the 7-day compressive strength is around 70% of 28-day compressive strength. In the lab, 7-day compressive strength was tested which must be higher than 38.25 MPa (80% of 45 MPa) to be on the safe side.

TABLE-US-00007 TABLE 7 Compressive Strength of Concrete at Various Ages Age Strength percent 1 day 16% 3 days 40% 7 days 65% 14 days 90% 28 days 99%

TABLE-US-00008 TABLE 8 Formula and results summary (experimental formula) Aggregate (g) Admixture 7-Day Fine aggregate Coarse (g) Dry compressive Binder (g) Coarse aggregate Water Water Height density strength OPC SCM Glass sand 10 mm (g) reducer (mm) (kg/m3) (MPa) 1 827 723.6 1343.8 413.5 289.4 2.8 80 2180 51.9 2 827 723.6 1343.8 413.5 289.4 1.4 80.2 2173 44.9 3 827 710.5 1319.4 451.1 289.4 1.4 80.3 2186 48.9 4 827 710.5 1319.4 451.1 289.4 0 81.1 2156 39.5 5 827 723.6 1343.8 413.5 289.4 0 81 2158 45 6 741.9 758 1407.7 432.8 259.7 1.4 81.3 2157 47.7

[0064] Commercial Site Trial

[0065] The formula is adjusted according to industrial feedback in a commercial setting. Aggregates are exposed on the ground without covering and no heating process is applied before mixing. The water-to-cement ratio is replaced by water-to-solid ratio displayed on a moisture indicator. It was found that the moisture indicator displays a lower value compared with the real moisture content. According to the record on site, the compositions of Table 9 were tabulated. (Remark: F/C ratio value here take 10% of 10 mm aggregate as fine aggregate).

TABLE-US-00009 TABLE 9 Composition and results summary (commercial trial formula) Aggregate (g) Admixture Fine aggregate Coarse (g) Binder (g) Coarse aggregate Water Water A/C F/C W/C OPC SCM Glass sand 10 mm (g) reducer ratio ratio ratio 1 862.7 443.5 1526.3 530.9 234.0 2.6 2.9 4.23 0.27  1* 822 422 1453 505 223 2.5 2.9 4.23 0.27 2 827 711 1320 451 252.9 1.5 3 5.11 0.306  2* 790 679 1261 431 241.7 1.4 3 5.11 0.306 3 747.2 763.5 1417.8 435.9 234.0 1.5 3.5 5.67 0.313  3* 709 724 1345 414 222 1.4 3.5 5.67 0.313 4 672 770 1432 489 218.5 1.5 4 5.11 0.325  4* 642 736 1368 467 208.7 1.4 4 5.11 0.325 5 834.9 717.8 1332.7 455.3 259.2 0 3 5.11 0.31

TABLE-US-00010 TABLE 10 Composition and results summary (commercial compositions) Dry density 7-Day compressive No. Height(mm) (kg/m.sup.3) strength (MPa) Sponsor's 1  79.7 2223.3 55.4 formula 1* 80 2146.8 49.6 A/C = 3.0 2  81.3 2281.2 51.7 2* 81.4 2202.2 39.9 A/C = 3.5 3  79.9 2180.9 49.6 3* 78 2117.1 42.2 A/C = 4.0 4  81.1 2122.4 39.2 4* 77.2 2072.1 35 A/C = 3.0; 5  80.5 2222.4 51.5 No SP

TABLE-US-00011 TABLE 11 Commercial trial results summary 7-Day 28-Day compressive compressive Passing-rate Passing strength strength Strength (Compressive rate (MPa) (MPa) percent strength) (Height) 1  55.4 56.7 98% 100%  100%  1* 49.6 50.2 99% 91% 89% 2  51.7 57.6 90% 86% 77% 2* 39.8 52.7 76% 86% 98% 3  49.6 55.5 89% 100%  100%  3* 42.2 56 75% 100%  11% 4  39.2 44.3 88% 34% 100%  4* 35 29.6 118%   0% 100%  5  51.5 60.4 85% 100%  98%

[0066] Composition No. 3 shows good properties. The average 28-day compressive strength is larger than 55.5 MPa. All the samples have a 28-day compressive strength more than 45 MPa and have a height within 80±2 mm. It is found that compressive strength at day 7 is around 90% of compressive strength at day 28 in this batch.

[0067] Water Absorption Characteristic Test

[0068] Since composition No. 3 satisfies the basic requirements, samples of this composition underwent further tests. The samples shall have a characteristic water absorption value not more than 6% by 24-hour cold water immersion method according to AS/NZ S 4456.14: 2003. The average cold water immersion water absorption is 3% showed in Table 12.

TABLE-US-00012 TABLE 12 Characteristic water absorption Specimen no. 4 5 6 7 8 9 10 11 12 13 Cold water 2.8 2.5 3.6 2.5 2.9 2.7 3.6 2.7 2.8 3.9 immersion water absorption (%) Average 3.0 cold water immersion water absorption (%)

[0069] The skid resistance value should be more than 60 according to the paving block requirements.

[0070] The average unpolished slip resistance value is 88 shown in Table 13.

TABLE-US-00013 TABLE 13 Unpolished slip resistance value Specimen Recorded individual Recorded individual Pendulum ID. readings at 0° readings at 80° value 22 87 88 88 87 87 88 88 87 88 87 88 23 88 87 87 88 87 87 88 87 88 88 88 24 87 87 88 88 87 88 88 88 87 87 88 25 88 87 87 88 88 87 87 88 88 87 88 26 88 87 87 87 88 87 88 87 87 87 87 Unpolished slip resistance value (USRV) 88

[0071] The average of compressive strength is 50 MPa and the characteristic compressive strength is 44 MPa shown in Table 14.

TABLE-US-00014 TABLE 14 The characteristic strength Identification mark 14 15 16 17 18 19 20 21 Lesser dimension of the two plan (L) (mm) 200 200 200 200 200 200 200 200 Nominal height (H) (mm) 79 79 79 79 79 79 79 79 Nominal gross plan area (A) (mm ) 19800 19800 19800 19800 19800 19800 19800 19800 Breaking Load (P) (kN) 1172 995 1134 994 1070 1168 1008 1140 Compressive Strength [00005]$C=\frac{1000P}{A}\times \frac{2.5}{1.5+L/H}\left(\mathrm{MPa}\right)$ 54 46 52 46 49 54 46 52 Square of Compressive Strength C.sup.2 (MPa.sup.2) 2883.7 2079.4 2704.0 2079.4 2410.8 2873.0 21344 2735.3 The Sum of Square of Compressive Strength ΣC.sup.3 (MPa.sup.2) 19900 Average of Compressive Strength C  (MPa) 50 Unbiased Standard Deviation [00006]$s=\frac{\sqrt{.Math.C\text{?}-n\left(C_m\right)\text{?}}}{n-1}\left(\mathrm{MPa}\right)$ 4 The Characteristic Strength of the Batch C  = C  − 1.65s (MPa) 44 indicates data missing or illegible when filed

[0072] Characterization of Efflorescence

[0073] Efflorescence Acceleration and Comparison

[0074] According to the Testing Standard ASTM C67-08 was Conducted Firstly to Evaluate the severity of efflorescence level by the naked eye. Prior to the tests, 5 control samples and 5 experimental samples were prepared, the detailed steps include:

[0075] Step 1: Immerse the samples in water having a depth of 25 mm for seven days.

[0076] Step 2: Put the sample in the environmental chamber without contact with water for seven days.

[0077] Step 3: Drying samples in the drying oven without contact with water for 24 hours.

[0078] Step 4: Observe and compare the efflorescence level.

[0079] In addition, in order to explore the possibility to accelerate the efflorescence progress in the concrete specimen, the depth of immersed water was raised from 25 mm to 100 mm and the time extended in contact with water from 7 days to 14 days.

[0080] Based on the optimized formula above, specimens were prepared for efflorescence comparison. As shown in the photograph of FIG. 8 almost no white deposit was found in the optimized formula (left) while a white efflorescence deposit leached out in conventional composition (right).

TABLE-US-00015 TABLE 15 Compositions for efflorescence comparison Cement Glass Sand 10 mm Water SP Conven- 2760.6 1419.2 4884.2 1698.9 748.8 8.3 tional composition Optimized 2256.7 2221.9 4123.6 2114.1 803.7 4.8 formula

[0081] Conductivity

[0082] According to the mechanism described before, the occurrence of efflorescence is mainly due to soluble ions in the concrete paving blocks. To evaluate the efflorescence potential, specimens were immersed in deionized water to let the soluble ions be diffused to the deionized water, including free calcium, sodium and potassium ions. Conductivity of the immersed solution was measured by conductivity meter, samples were immersed in same containers with the same volume of deionized water, and measured in day 3, day 7 and day 14 until reaching a stable ion concentration.

[0083] Based on the optimized composition, compositions containing fly ash and glass powder in Table 16 were set to measure the conductivity; the corresponding results were showed in FIG. 9 and FIG. 10, respectively.

[0084] Generally, the conductivity initially increased within first 7 days then tended to be stable afterwards. Among these groups, the addition of 5% fly ash can reduce as high as 34% in the conductivity.

TABLE-US-00016 TABLE 16 Formula for conductivity comparison Cement FA or GP Glass Sand 10 mm Water SP Conven- 2760.6 1419.2 4884.2 1698.9 748.8 8.3 tional 1 2256.7 2221.9 4123.6 2114.1 803.7 4.8 2 2200.3 56.4 (2.5%) 2221.9 4123.6 2114.1 803.7 6.5 3 2125.9 112.8 (5%) 2221.9 4123.6 2114.1 803.7 8 4 1974.7 169.2 (7.5%) 2221.9 4123.6 2114.1 803.7 8.5 5 2031.1 225.6 (10%) 2221.9 4123.6 2114.1 803.7 9.5

[0085] As compared to fly ash groups, glass powder performed worse in efflorescence reduction, only 21% in Day 7 in the case of 2.5% glass powder. The conductivity tended to increase after Day 7 (as shown in FIG. 10) which may be caused by high reactivity of ultra-fine glass powder, leading an earlier balance of ion concentration.

[0086] Water Absorption

[0087] Water absorption indicates the permeability of paving blocks. More pores inside the concrete paving blocks can not only absorb more water, but also create path for soluble ions migrating to the surface of concrete blocks. Additionally, outside water (raindrops and dew) can penetrate easily into the concrete blocks which causes the secondary efflorescence.

[0088] To demonstrate the effect of ultrafine glass powder or fly ash, samples were prepared according to the compositions listed in Table 17.

TABLE-US-00017 TABLE 17 Compositions for water absorption test Cement FA or GP Glass Sand 10 mm Water SP conven- 2760.6 1419.2 4884.2 1698.9 748.8 8.3 tional 1 2125.9 112.8 FA 2221.9 4123.6 2114.1 803.7 9.5 2 2125.9 112.8GP 2221.9 4123.6 2114.1 803.7 9.5

[0089] It can be seen from Table 18 that the conventional composition had the largest water absorption value among these groups (3.91%) while 5% GP+9.5 g SP formula had the lowest water absorption (2.5%). In addition, glass powder group has a smaller value as compared to the fly ash groups due to the higher reactivity.

TABLE-US-00018 TABLE 18 Water absorption test results Formula 1 h 2.5 h 5 h 10 h Sponsor (8.3 g SP) 3.80% 3.83% 3.90% 3.91 5% FA + 9.5 g SP 2.50% 2.94% 3.10% 3.13 5% GP + 9.5 g SP 1.83% 2.27% 2.43% 2.50

[0090] Fly Ash Content:

[0091] To further enhance the quality of concrete paving block, in terms of the long-term compressive strength and control the efflorescence, fly ash and glass powder (<75 microns) were proposed to be used in this project. Given the fact that glass powder (<75 microns) can accelerate the cement hydration at early stage, research focus in the supplementary cementitious material was fly ash. Table 19 showed the different replacing ratio of cement by fly ash, from 0 wt. % to 10 wt. % and their corresponding 28 days compressive strength.

TABLE-US-00019 Different replacing ratio and the corresponding 28-day compressive strength 28-Day compressive Cement Fly ash Glass Sand 10 mm Water SP strength (MPa) Mix 1- 2256.7 0 2221.9 4123.6 2114.1 803.7 4.8 46 0% Mix 2- 2200.3 56.4 2221.9 4123.6 2114.1 803.7 6.5 45.4 2.5% Mix 3- 2125.9 112.8 2221.9 4123.6 2114.1 803.7 8 41.1 5% Mix 4- 1974.7 169.2 2221.9 4123.6 2114.1 803.7 8.5 40.6 7.5% Mix 5- 2031.1 225.6 2221.9 4123.6 2114.1 803.7 9.5 44.4 10%

[0092] As can be concluded from the table, compressive strength decreased with greater replacement of cement due to the low reactivity of fly ash. However, there is no obvious change in the compressive strength. Considering that the compressive strength in last plant trial (44 MPa) was very close to the design strength (45 MPa), compressive strength can be further enhanced by water spraying curing. Hence, substituting cement by fly ash within a certain range (e.g., 5%) can be a promising way to maintain sufficient strength and control the efflorescence.

[0093] It should be apparent to those skilled in the art that many modifications besides those already described are possible without departing from the inventive concepts herein. The inventive subject matter, therefore, is not to be restricted except in the spirit of the disclosure. Moreover, in interpreting the disclosure, all terms should be interpreted in the broadest possible manner consistent with the context. In particular, the terms “include”, “including”, “comprises” and “comprising” should be interpreted as referring to elements, components, or steps in a non-exclusive manner, indicating that the referenced elements, components, or steps may be present, or utilized, or combined with other elements, components, or steps that are not expressly referenced.