Physico-mechanical, Chemical and Durability Characteristics of Mortar and Concrete Containing Palm Oil Boiler Clinker Aggregate Blended with Rice Husk Ash and Ca-Bentonite

Abstract

This research focused on utilization of palm oil boiler clinker (POBC) as a whole natural aggregate substitution blended with calcium bentonite (CB) and rice husk ash (RHA) for green mortar and concrete productions. The CB and RHA were partially replaced by weight of ordinary Portland cement (OPC), type 1 in three proportions of 10%, 20%, and 30% for binary and ternary blends. All mixtures were taken constant water to binder ratio of 0.48. The behavior of fresh pastes on Vicat setting times and hydration temperature were investigated. The microstructure and mineral phase compositions of mortars were characterized via scanning electron microscope (SEM) and X-ray diffraction technique (XRD). All mortar specimens were cured in lime-saturated water at ambient temperature of 29 ± 3 ºC, RH = 80-90% for periods of 7, 28, and 56 days before each testing. The harden specimens were casted for examination in these following properties: water absorption, apparent porosity, compressive strength, sulfuric acid and sodium sulfate resistance. The cylindrical concrete specimens were prepared for rapid chloride ion permeability test (RCPT), capillary water absorption, and indirect tensile strength test (Brazilian test). As a result, it was observed that the POBC aggregate can be potentially substituted natural aggregate for mortar and concrete productions. The setting times, hydration temperature of pastes, and percentage flow of fresh mortars were reduced with an increase in binary and ternary blends. The maximum reduction in setting time and hydration temperature was 16% and 14% for the mix incorporating up to 30% RHA. Consequently, an increase in RHA up to 30% decreased the percentage flow by 38%. Moreover, the compressive strength decreased as an increase in ternary blends with prolonged curing ages, the 56-day highest compressive strength was 53 MPa for the mix incorporating 20% RHA. The durability performances of mortar including water absorption and porosity, sulfuric acid and sodium sulfate resistance improved with an increase in RHA replacement level up to 30% and up to 56-day curing ages. The lowest deteriorating due to sulfuric acid attack was suppressed 0.47% loss in weight and 1.58% loss in compressive strength for the mix incorporating 30% RHA cured for 56 days, as well as the lowest percentage gain in weight and loss in compressive strength due to sodium sulfate attack was 0.03% and 0.32%. The SEM microstructure and XRD patterns of dominant mortars specimens indicated that flocs-like and fibrous-like forms of the C-S-H densely formed in the matrix and filled up the pores of the mortar containing RHA compared to that of control mix, binary and ternary mixes incorporating CB. This findings contributed to the strength and durability improvement. Likewise, an increase in RHA replacement level and curing ages reduced the chloride ion penetrability and capillary absorption coefficient of the concretes containing POBC as a coarse aggregate, while an increase in CB increased those one. The lowest chloride ion penetrability and capillary absorption coefficient was 336 coulombs and 0.06 kg/mm2/h0.5 for the mix incorporating up to 30% RHA at the age of 56 days. The indirect tensile strength of concrete increased with curing ages. The highest indirect tensile strength was 3.80 MPa for the mix incorporating 10% RHA. Therefore, considering in view of practical implication according to the experimental results and waste exploitation, the performances of green mortar and concrete produced with POBC as an aggregate replacement can be improved by the optimum incorporation of binary mixtures of up to 10% CB, 30% RHA, and ternary mixtures of up to 5-10% CB with 10-20% RHA.