Initial Surface Absorption of Cement Combination Concretes at Equal Strengths
Figures 7 and 8 show that cube compressive strengths of concretes at 28 days reduced with increasing water/cement ratio.
Since concrete is specified in practice on the basis of strength at 28 days, ISAT 10 values of the concretes were examined at equal 28-day strengths.
In a marine environment, in addition to its presence in original mix, the chloride ions penetrate into the concrete either from sea water or sea winds carrying sea salts and reacts with the hydrated cement products which produces complex compounds including Friedels salt which are leachable and expansive in nature.
In the regions with a cold climate, the freeze-thaw damage is the most important issue among the durability problems in concrete structures, such as dams, hydraulic and offshore structures, and bridges and highway pavements, during their service (Rao et al.
Fly ash combines with calcium hydroxide to produce additional cementitious materials, thereby reducing the amount of calcium hydroxide that may be leached out of the concrete. Leaching of the calcium hydroxide increases concrete voids which can accelerate freeze-thaw damage.
A Chinese standard (GB/T1596-2005)  Grade I fly ash was used as admixture to make the concrete. A Chinese standard (GB/T21120-2007)  polypropylene fiber was used to make the concrete, the length of which was 19 mm.
A series of cubic concrete specimens with the size of 100 mm x 100 mm x 100 mm were cast including ordinary concrete, fly ash concrete, and double-mixture concrete.
The concrete specimens cured for 28 d were immersed in the solutions of [Na.sub.2]S[O.sub.4] and [(N[H.sub.4]).sub.2]S[O.sub.4], respectively, and separated by some wooden bars each other.
Utilization of ceramic waste as fine aggregate within Portland cement and fly ash concretes. Cement and Concrete Composites 32: 440449 (2010).
Therefore use of ceramic waste as partially replacement material of any of constituents of the concrete will not only control the product waste tactfully but will also economize concrete manufacturing cost.
Concretes with aggregates from demolition waste and silica fume.
Fresh properties of NCA and RCA concretes Fresh property NCA concrete RCA concrete Workability Slump (mm) 90-275 70-255 Slump flow (mm) 600-735 380-725 Slump loss for normal 50 75 concrete (after 45 min) (%) Slump loss for self- 2.4-2.6 7.4-10.4 consolidating concrete (after 1 h) (%) Stability (segregation resistance) Visual stability index, [VSI.sub.NCA] [less [VSI.sub.RCA] [much VSI (a) (based on than or equal less than] 1 bleeding, mortar halo, to] 1 and aggregate piling) Sieve segregation (%) 8.9-10.4 8.3-12.3 Wet density 2325-2455 2250-2370 (kg/[m.sup.3]) Air content (%) 1.3-6.3 1.5-6.9 (a) A lower VSI value indicates higher stability or segregation resistance.
As shown in Table 2, the water to cement ratios of 0.47 and 0.53 are determined depending on the mixture proportions of control concrete. Mixture proportion of recycled aggregate concrete is obtained by using recycled coarse aggregate as the same weight to replace the natural aggregate of the control concrete at 16.7%, 33.3%, 50%, 66.7%, and 100%.
where [DELTA]W is the additional water consumption in concrete mixture; [m.sub.RA] is the mass of recycled aggregate in concrete; [w.sub.RA] and [w.sub.OA] are the water contents of recycled aggregate and ordinary aggregate, respectively; [s.sub.RA] and [s.sub.OA] are the water absorption of recycled aggregate and ordinary aggregate, respectively; [m.sub.A] is the mass of recycled concrete; and a is the percentage of recycled aggregate in the total aggregate of concrete.