The Evolution of Concrete (Part 2): Unprotected in Humid Tropical Weather and Its Compression Strength

Abstract

This paper discusses the unprotected concrete in the basement which has been neglected for 10 years. The purpose of this study was to determine the compressive strength and microstructural changes in unprotected concrete in the humid tropics. The research was carried out experimentally. It was a case study at the State University Hospital, Lampung University, Indonesia. The compressive strength and microstructure of unprotected concrete compared to concrete in the protected condition. The compressive test samples were taken with 4 core drills for each condition. The compression test data was processed by the Outlying method. The microstructure of the concrete was examined by scanning electron microscopy (SEM), and energy-dispersive X-ray (EDX). The results showed that the compressive strength of unprotected concrete was 65% of the compressive strength of protected concrete. There are Kalium (Potassium) compounds in unprotected concrete but not in protected concrete. Rain that enters the unprotected concrete makes Ca dissolve and the porosity increases. Oxidized Potassium in the air enters the concrete, increasing oxidation, and producing calcite. Calcite dominates the microstructure of unprotected concrete. Oxidation causes the pH to decrease and silica dissolves. This makes CSH and CH unstable. Ca bonds in unprotected concrete are more easily broken. The presence of Potassium and the hot air of the tropics makes the temperature in the concrete increase, the expansion of Al and calcite becomes greater and the microstructure of the unprotected concrete becomes complex. Cracks appear in the unprotected concrete microstructure.  The inclusion of elements that are reactive to the concrete can make the concrete degraded.

Keywords: compressive strength, concrete, evolution, microstructure, tropical weather, unprotected

DOI: 10.7176/CER/14-4-02

Publication date:June 30^th 2022