Dealing with workability loss challenge in SCC mixtures incorporating natural pozzolans: A study of natural zeolite and pumice

Substituting portland cement with natural zeolite (NZ) and pumice in self-consolidating concrete (SCC) is used to improve the workability and hardened properties of mixtures. The workability retention of SCC incorporating these natural pozzolans has remained a challenge in the literature. In this study, different methods of workability retention improvement on the natural pozzolan-SCC mixtures were investigated. These methods include the use of polycarboxylate with larger molecular weight and side chain density, retempering with superplasticizer (SP), retempering with withhold water, and a combination of retarder and SP. The fresh and hardened properties of the NZ and pumice-incorporated mixtures were investigated through measuring workability retention, setting time, and compressive strengths, in two ratios of water-to-cementitious materials (w/cm). Results show that the SCC mixtures incorporating NZ had lower setting time in comparison to the SCCs without natural pozzolans, although the setting time of SCC contained pumice increased. The NZ-incorporated SCCs required a higher dosage of SP for retempering however the pumice contained SCCs required lower SP than the reference due to the low-polymer adsorption of pumice-blended cement. The slump loss in SCC mixture without pozzolan (Ref-0.36) was more severe than the mixtures containing NZ. The reduction in compressive strength of mixtures treated with different retempering methods was insignificant but more tangible when superplasticizer and retarder were used. A larger quantity of SP was required for retempering the SCCs with retarder and SP compared with the those retempered with SP only. The increase or decrease in the SCC compressive strength in case of using retarder and SP for SCC retempering purpose was dependent on the amount of pozzolan replacement and the w/cm ratio in the mixtures. Overall, in w/cm ratio of 0.40, the SCC mixtures incorporating 10 and 15% NZ and pumice, respectively, possessed as the optimal mixtures considering the slump loss and the compressive strength. (C) 2019 Elsevier Ltd. All rights reserved.