This research identifies the relative humidity effect and the optimum mixing method for Self-Compacting Concrete (SCC) containing OPC mixed with agro-industrial wastes of palm oil fuel ash (POFA) and low calcium based fly ash (FA). The effects of temperature and relative humidity on the fresh state properties were assessed under three conditions; moderate humidity, H1 (RH of 70 to 80% with temperature of 32°C) and low humidity, H2 (RH of less than 70% with temperature of 36°C) and extremely high humidity, monsoon season, H3 (RH of more than 80% with ambient temperature around 23 ±2°C). Six types of mixing method were evaluated for the ternary blended mix (TNY40) with two types of super-plasticiser (SP) additions: simultaneous and delayed, in order to discover the optimum mixing time and loading sequence. Furthermore, the slump flow retention was recorded every 15 minutes after batching. In conclusion, it was found that the increased temperature with lower relative humidity accelerates the reduction of workability (up to 15%) especially in POFA SCC as compared to FA and TNY (8%) samples. From the evaluation of various mixing method, the optimum mixing method observed was using the delayed addition of SP with a total mixing time of 12 minutes. This method resulted in excellent workability properties and with mixes retaining its slump within 15 minutes of batching.
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