Abstract In this study, the effects of coarse pumice aggregate (CPA) treatment with alkyl alkoxy silane (AAS) and direct addition of AAS as an admixture at different dosages on workability, water requirement, early strength development and water absorption of pumice concrete blocks have been investigated. The AAS treatment greatly enhanced the workability in an indirect way; the need for extra mixing water was significantly decreased. The performance of external silane addition was not as effective as in the case of surface treatment method. AAS treatment reduced the impregnation of water into the CPA and let the free water to increase the consistency as a lubricating agent between aggregates and paste matrix. Additionally, AAS treated CPA incorporating mixtures showed excellent behavior both in obtaining better workability and achieving higher early strengths compared to control mixture. The effectiveness of AAS surface treatment on reducing the water/cement ratio also causes an increase in ultimate strength of pumice concrete blocks. SEM micrographs and MIP analysis of AAS treated and untreated CPA incorporated concretes showed that, the matrix phase of AAS treated CPA incorporated pumice block was denser than untreated ones. Coarser porosity of matrix phase of untreated CPA can be attributed to the quick water absorption of CPA, which reduced the consistency of matrix to obtain sufficient compaction.