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

Abstract

ACI 237R – 07 defines Self-Compacting Concrete (SCC) as “a highly flowable, non-segregating concrete that can spread into place, fills the formwork, and encapsulates the reinforcement without any mechanical consolidation”. The salient characteristics of SCC include high deformation and high resistance to bleeding and segregation, the two opposite properties that are to be met with. Applications of SCC includes placements that have congested and heavy reinforcements such as pile foundations, raft foundations, bridge piers, tunnel linings, skyscrapers, aircraft runways, pre-stressed concrete sections and transportation structures etc. SCC is known for their uniform compaction and hence uniform durability. The aim of this research was to know the response of SCPs using partial replacement of Cement by Fly Ash (FA) and Limestone Powder (LSP) under the influence of variable mixing water temperature. The parameters investigated were Water Demand (WD), Super Plasticizer Demand (SPD), Initial & Final Setting Times, Flow Times, Compression and Flexure Strengths of prisms having dimensions of 4x4x16 cm at 1, 3, 7, 28 and Calorimetry. Test results showed an overall increase in WD (w.r.t % W/C, cement mass) as percentage replacement of SRMs increased because of small particle size of SRMs, which increases the total powder surface area. SPD (% cement mass) also increased for the target flow of 30±1 cm when the replacement percentage of OPC by SRMs was increased. Formulations were cast, cured and tested in SSD condition as per EN 196-1 standards. The early strength of SCP formulations containing FA decreased as compared to that of pure OPC and LSP. However, 28 days strengths of formulations containing FA are appreciably high. It can be explained due to the pozzolanic behavior of FA. LSP gave higher early strengths than OPC and FA. 20% replacements of OPC by FA and LSP have shown highest compressive strengths among all FA and LSP formulations. Therefore, FA20 and LSP20 were selected for studying the response of variable mixing water temperatures. To match the average climatic conditions of Pakistan, control temperature of 20°C was selected. A lower temperature of 10°C and a higher temperature of 30°C were selected. SP demand (% cement mass) tends to decrease with increase in temperature. Generally, temperature of 30°C showed more compressive strengths. v The overall outcome of this study is the affirmation of the positive outcomes of SRM replacement in terms of strength, flowability and segregation-resistance. Cement production could be minimized due to SRM replacements and as a result, CO2 emissions would reduce. Subsequently, we end up with a product having more strength, workability, segregation resistance, flowability than conventional concrete that can be used on large scale placements, reducing both labor cost as well as section dimensions.