Mix Design of High-Strength Concrete Incorporating Spherical and Crushed CRT Funnel Glass Waste

Abstract

Cathode ray tube (CRT) funnel glass, due to its high content of lead oxide (PbO), is considered as hazardous waste. The growing volume of the disposed CRTs technology presents a risk of environmental contamination owing to the potential of toxic Pb metals leaching from glass. A typical way of recycling CRT funnel glass waste is by crushing it and partially replaced the cement and fine aggregates. However, this approach has been facing serious issues in terms of leaching of Pb. Hence, a new recycling method has been developed, that is by performing proper melting and annealing operations in producing the spherical CRT funnel glass (GS). GS does not show any harmful risk of the release of Pb to the environment. The Pb leaching value of CRT concrete specimens with GS is significantly lower than the allowable limit although it contains high concentration of PbO, 25%. While the performance of GS in leaching aspects have been determined, the optimum mix designs of high-strength concrete incorporating both GS and crushed CRT funnel glass (GC) as coarse aggregates yet remains to be investigated. Predominantly to provide a safe method of recycling CRT funnel glass as aggregate and to increase the confidence level of the industries, this paper addresses the mix design of high-strength concrete with GS and GC as coarse aggregates. Given the importance of selecting the materials and its contents, the influence of five parameters, i.e. water/binder (w/b) ratio, coarse aggregate (CA) content, superplasticizers (SP) dosage, and silica fume (SF) content were evaluated. It was found that the incorporating of GS and GC that differ in terms of morphologies (size, shape, texture) and water absorption rate than the natural rock have led to the increase of workability of CRT concrete mixtures, however, decrease the compressive strength. But the results also have highlighted that the CRT specimens that were designed with w/b ratio 0.31, 43% content of CA, 2% SP, and 10% SF were able to achieve the highest strength of 61 MPa, which was only 9% lower than control specimens. The optimum mix design of CRT concrete has greatly improved the strength of concrete and enhance its potential for future applications.