HRWRHigh-Range Water Reducer (concrete admixture)
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The mix design parameters included in the database were the relative amounts, in kg/[m.sup.3], of water, cement, limestone powder, fly ash, silica fume, slag, sand, coarse aggregate, superplasticizer or high-range water reducer (HRWR), and viscosity-modifying admixture (VMA) and the maximum aggregate size, in mm.
In summary, the contour plots in Figure 3 prove that, to attain good flowability, the following recommendations are valid in general: (i) there is no need to increase water content beyond 190 kg/[m.sup.3]; (ii) for cement contents between 350 kg/[m.sup.3] and 500 kg/[m.sup.3], the dosage of SCMs should not be higher than 100 kg/[m.sup.3]; (iii) HRWR dosages below 1.6% over weight of cement should suffice; and (iv) when SCMs are added above 100 kg/[m.sup.3], the use of VMA is necessary.
The effect of HRWR dosage, on the contrary, is of more significance.
All solid ingredients including PC, MK and fine aggregates are firstly mixed together for the first 2min, then water and HRWR are added into the dry mixture and mixed for another 2min.The fibers are slowly added to the concrete and later demoulded after 24hrs.
ECC Cement (C) (kg/[m.sup.3]) 650 Fly ash (FA) (kg/[m.sup.3]) 325 Water (W) (kg/[m.sup.3]) 375 PVA fiber (kg/[m.sup.3]) 26 Sand (kg/[m.sup.3]) 480 HRWR (kg/[m.sup.3]) 12 HPMC (kg/[m.sup.3]) 1.90 W/(C + FA) 0.38 FA/C 50% 28-day tensile strain (%) 3.5 28-day tensile strength (MPa) 3.3 TABLE 2: Two cooling regimes for different curing-age ECC specimens.
The presence of HRWR also tends to destabilize the entrained air bubbles during transport and placement of concrete leading to a reduction in air content (Khayat and Assaad 2002; Safiuddin et al.
In addition, a polycarboxylate-based HRWR and a synthetic AEA were used to produce the required flowing ability and air content, respectively.
Preliminary results from the New Mexico test sites show that Class F ash, Lomar (HRWR), or blended Class C and F ashes may improve resistance to ASR distress.
Mix Mix Cement Sand LA HRWR AEA CE Water group code 1-1 450 729 737 4.50 0.05 0.23 225 Set (1) 2-1 450 729 737 4.50 0.05 0.23 203 3-1 450 729 737 4.50 0.05 0.23 180 1-2 435 705 737 4.35 0.04 0.22 218 Set(2) 2-2 435 705 737 4.35 0.04 0.22 196 3-2 435 705 737 4.35 0.04 0.22 174 Table 5: Testing results of compressive strength and unit weight.
Steel fibre addition showed reduction in workability and was reinstated with the addition of high range water reducing (HRWR) admixture.
Coarse aggregate Binder (B) kg/[m.sup.3] Fine aggregate (CA)-mortar (M) % (FA) kg/ Cement Slag [m.sup.3] CA 60%-M 40% 225 225 705.26 Coarse aggregate Coarse aggregate Water/binder Chemical (CA)-mortar (M) % (CA) kg/ ratio admixture [m.sup.3] (HRWR) CA 60%-M 40% 1258.34 0.3 1% TABLE 3: Detailed mixture proportions for various concretes with coarse aggregate 60% and mortar 40% and different fibre dosages.
This chemical admixture is also known as a high range water reducer (HRWR) and supplied by a local manufacturer which is the polycarboxylic ether (PCE) based.