GROUND PUMICE as PARTIAL REPLACEMENT of CEMENT in RIGID PAVEMENT

Abstract

Pumice is widely available pozzolanic material in the vicinity of the rift valley zone in Ethiopia where a significant amount of construction activities takes place. In addition to its abundance, its ease of crushing encourages contractors to utilize it. This research aims at studying the range of application of raw Ground pumice as a partial replacement of Ordinary Portland cement for concrete rigid pavement in respect of strength, heat of hydration and durability. Strength and effective permeability experiments were conducted for mixtures having 0-40% volume based Ground pumice replacement at 5% increment. Following the review of previous studies and the identification of a maximum partial replacement percentage of 15% in respect of strength, water depth permeability, semi adiabatic, and simulating experiments were carried out on replacement percentages of 0%, 10%, 15%, and 20%. Except for replacements at 20%, 25%, 30%, 35%, and 40%, replacements in the 5%, 10%, and 15% range result in an increase in compressive strength compared to replacement with ground pumice (control group). However, the compressive strength of blended mixture with 20% replacement satisfies the minimum target strength of C-30 concrete in the absence of historical data. Therefore, even if a slight 28th day strength drop noticed, ground pumice could partially replace the cement up to level of 20%. In addition to strength enhancement, the experiment revealed that Ground pumice in the concrete mixture reduces the total heat of hydration, and decreases the thermal gradient in the specimens. Despite insignificant drop observed on water permeability experiments on all replacement range, Ground pumice replaced mixtures demonstrated remarkable result against minimum threshold value of National and international standards. Using Hacon3 finite element model (FEM) tool, heat of hydration and thermal cracking risk were also simulated. The FEM result indicates a good level of agreement with temperature rise of laboratory readings. For concrete at all replacement percentages, the temperature rise was decreased as the proportion of replacement has increased. The simulated hygrothermal slab panel reveals induced thermal stress due to early age hydration decrease with an increase in replacement percentage of ground pumice. Finally, it is recommended to investigate pumice as cement replacement material under the guidance of ASTM designation C-1709,"Technical approach to the evaluation of alternative supplemental cementitious materials."