1874-1495/21 Send Orders for Reprints to reprints@benthamscience.net 370 DOI: 10.2174/1874149502115010370, 2021, 15, 370-380 The Open Civil Engineering Journal Content list available at: https://opencivilengineeringjournal.com RESEARCH ARTICLE Effect of Waste Clay Brick Powder on Physical and Mechanical Properties of Cement Paste David Sinkhonde 1,* , Richard Ocharo Onchiri 2 , Walter Odhiambo Oyawa 3 and John Nyiro Mwero 4 1 Department of Civil and Construction Engineering, Pan African University Institute for Basic Sciences, Technology and Innovation, Nairobi, Kenya 2 Department of Building and Civil Engineering, Technical University of Mombasa, Mombasa, Kenya 3 Department of Civil, Construction and Environmental Engineering, Jomo Kenyatta University of Agriculture and Technology, Nairobi, Kenya 4 Department of Civil and Construction Engineering, University of Nairobi, Nairobi, Kenya Abstract: Background: Investigations on the use of waste clay brick powder in concrete have been extensively conducted, but the analysis of waste clay brick powder effects on cement paste is limited. Materials and Methods: This paper discusses the effects of waste clay brick powder on cement paste. Fragmented clay bricks were grounded in the laboratory using a ball mill and incorporated into cementitious mixes as partial replacement of Ordinary Portland Cement. Workability, consistency, setting time, density and compressive strength properties of paste mixes were investigated to better understand the impact of waste clay brick powder on the cementitious paste. Four cement replacement levels of 2.5%, 5%, 7.5% and 10% were evaluated in comparison with the control paste. The chemical and mineral compositions were evaluated using X-Ray Fluorescence and X-Ray Diffractometer, respectively. The morphology of cement and waste clay brick powder was examined using a scanning electron microscope. Results: The investigation of workability exhibited a reduction of slump attributed to the significant addition of waste clay brick powder into the cementitious mixes, and it was concluded that waste clay brick powder did not significantly influence the density of the mixes. In comparison with the control paste, increased values of consistency and setting time of cement paste containing waste clay brick powder confirmed the information available in the literature. Conclusion: Although waste clay brick powder decreased the compressive strength of cement paste, 5% partial cement replacement with waste clay brick powder was established as an optimum percentage for specimens containing waste clay brick powder following curing periods of 7 and 28 days. Findings of chemical composition, mineral composition and scanning electron microscopy of waste clay brick powder demonstrated that when finely ground, fragmented clay bricks can be used in concrete as a pozzolanic material. Keywords: Waste clay brick powder, Cement paste, Workability, Setting time, Compressive strength, Pozzolanic materials. Article History Received: March 03, 2021 Revised: June 30, 2021 Accepted: July 7, 2021 1. INTRODUCTION The inclusion of pozzolanic materials in cement paste has attracted increasing interest due to its acceptable performance in compressive strength, which sometimes outweighs that of * Address correspondence to this author at the Department of Civil and Construction Engineering, Pan African University Institute for Basic Sciences, Technology and Innovation, Nairobi, Kenya; Tel: 0748328287; E-mail: davidsinkhonde@gmail.com conventional paste. A vast amount of literature has evaluated the impact of several pozzolanic materials on cement paste, including magnetic-silica, nano-magnetic and nano-silica [ 1, 2], fly ash [ 3, 4], metakaolin [5] and silica fume [ 6, 7]. An exhaustive cement paste literature review undertaken has shown that the influence of Waste Clay Brick Powder (WCBP) on workability, consistency, setting time, density and compressive strength of cement paste has received little attention. Comprehensive information regarding the behaviour