INFLUENCE OF BLENDS OF FLY ASH AND LIMESTONE POWDER ON THE PROPERTIES OF SELF-COMPACTING PASTE SYSTEMS UNDER VARIABLE MIXING WATER TEMPERATURE

Abstract

Self-Compacting Concrete (SCC) is a modern concrete system characterized by high flowability and high segregation resistance without mechanical vibration. ACI 237R – 07 defines SCC as “a highly flowable, non-segregating concrete that can spread into place, fill the formwork, and encapsulate the reinforcement without any mechanical consolidation”. SCC incorporates higher percentage of cementitious powders, lower w/p, and a super-plasticizer. This yields a workable, denser, durable and stronger concrete. There are various applications of SCC based on these characteristics, namely the heavy raft foundations, bridge piers, pavements, runways, tunnel linings, immersed tunnels and heavily reinforced sections. In this study, the Self-Compacting Paste Systems (SCPS) have been studied as they control the properties of SCC both in fresh and hardened states and act as vehicles for the transport of aggregate during its flow. The study gives the comparative response of partial replacement of Ordinary Portland Cement grade-53 by the Secondary Raw Materials (SRMs) i.e. Fly ash (FA) and Limestone Powder (LSP) in Self-Compacting Paste Systems (SCPS) and the influence of mixing water temperature variation on the response of such systems. The parameters studied were the water demand (WD), super-plasticizer demand (SPD) for target flow of (30 ± 1) cm, flow times, initial and final setting times, calorimetry, and strengths of 4*4*16 cm prisms at 1, 3, 7, and 28 days of age. There were two aspects of this research. First was to determine the optimum replacement percentage of cement by equal mass blends of FA and LSP; second was to study the response of SCP systems to mixing water temperature variation at optimum replacement percentage. The five mix proportions were considered; a neat self-compacting paste and 10, 20, 30 and 40 percent of cement replacement with equal mass blends of FA and LSP. The water requirement of the system increased if calculated as the w/c, while it decreased when calculated as w/p. SPD increased with increase in quantity of finer SRMs in system. Setting times and calorimetry showed that hydration was retarded by addition of blend of SRMs. Mixes were cast at WD of the respective system, cured and tested as per EN 196-1 in dual chamber. SRMs increased the 28-day strength of SCP systems up to 30 percent replacement, while 40 percent OPC replacement gave lower strength than the neat SCP. The highest strengths of SCP system were at 20 and 30 % cement replacement by blend of FA and LSP because of finer particle size of SRMs and the better packing density. These systems were then studied for the three mixing water temperature variations i.e. 10, 20 and 30 °C. While, water demand, w/c stayed constant for neat paste system, it increased for 20% and 30% cement replacement by blend of SRMs at 30 °C water. SPD increased for the systems as the mixing water temperature was lowered; there was a considerable high SP demand at 10 °C mixing water. A linear trend was observed with setting times; decrease in water temperature retards the initial and final setting. Using mixing water at higher temperature, the rate of release of heat of hydration in all systems increased. Consequently, peaks in the calorimetry curves occurred much earlier for the higher mixing water temperature. However, compressive strengths reduced for the paste systems as the water mixing temperature was varied from the (20 ± 1) °C. Flowable and self-compacting concrete can be thus produced, conserving the natural resources, utilizing industrial waste, minimizing the compaction labor and costs and having a workable, pumpable, segregation-resistant mix with high strength and durability.