ACI SP-209

Abstract

<strong>Synopsis:</strong>&#160; This paper provides results of different types of curing in hot weather environment on the compressive strength of concrete made with portland cement and complementary cementitious materials (CCM) such as natural pozzolans, fly ash (FA), granulated blast furnace slag (GBFS), and silica fume (SF). In all concrete mixtures, a superplasticizing admixture (SPA) was used. <br>Nine series of concrete mixture were made. In seven of them (1,2, 3,4,5, 6 and 9) the normal portland cement (NPC) content was 200 kg/m³ and in two of them (7 and 8) the same amount of cement was used but it was a portland-natural pozzolan cement (PNPC). The CCM varies from 9.9 to 60.6% of the total cementitious material. The W/C in all series was 0.70 when using NPC or PNPC. The W/C+CM varied from 0.28 to 0.63. In all series the same amount of 1260 kg/m³ of coarse aggregate was used. <br>Five different ways of curing were used. One was the initial and final ASTM curing at 23&#176;C up till the age of testing as reference, and four different ways of curing in hot weather environment at 37&#176;C for the first 24h were used. These final curings were: A) ASTM; F) three day and G) seven-day water spray for 15 minutes every 2h; and (E) covered by two layers of membrane. <br>Adequate compressive strength development (CSD) can be obtained using CCM but very good curing is necessary. Generally, by casting specimens at 37&#176;C and put them under ASTM curing next day at 23&#177;2&#176;C (A), the strength at 28 days was lowered by about 8% and at six months by about 8% lower than these casting at 23&#176;C. <br>Membrane curing was less effective at later ages mainly when fly ash was used. There exist an optimum amount of fly ash to obtain maximum compressive strength at later ages.