Eco-friendly mortar using wood ash and crumb rubber as partial replacements for cement and sand

Abstract

1 (Wood Ash): Concrete is the most common product used for construction purposes in the modern era. One main component in concrete mixing is cement, a material which production causes huge carbon dioxide emissions into the air resulting in a major pollution concern. Amid fears of increasing pollution, researchers have suggested the potential use of renewable wastes to replace cement in concrete and mortar production, where wood ash was highly considered due to its pozzolanic properties. Wood ash is the product of combustion of forest residues that produces power and heat. It is mostly disposed through landfilling which is a costly and dangerous process, not to mention that landfilling areas are diminishing. The purpose of this project is to study the effect of replacing cement by wood ash obtained from a local bakery on the flexural strength, the compressive strength, and the slump/flowability of the resulting mortar mix. A reference mix with 0% wood ash, as well as mixes including 2%, 4%, 6%, 8%, 10%, 15%, and 20% wood ash as cement replacement were prepared. The effect is expected to be similar on concrete mixes, since the element being replaced, that is cement, is present in both mortar and concrete (concrete is mortar mixed with coarse aggregates or gravel with varying percentages). The compressive and flexural strength were studied at 7, 14, and 28 days, while the slump was measured immediately following the fresh mixing process. The results showed that up to 10% percent of cement replacement by wood ash still yields a compressive strength exceeding 20 MPa; however, at percent replacements of more than 10%, a decrease in early and late mechanical strength (compression and flexure) became much more evident. The increasing wood ash presence also resulted in a gradual decrease in the mortar flowability. The mix with an imposing wood ash percentage that gave a combination of acceptable early and late strength (lightweight concrete) as well as acceptable flowability was found to be the one with 10% replacement, which will be considered the optimum mix.

2 (Crumb Rubber): Recently, dangerous problems are caused to the society due to of the increasingly amount of glass, plastic, and rubber waste. The huge amount of these wastes is causing pollution. One of the best solutions to get rid of the danger caused by them is "Recycling". This problem can also be solved by diminishing their usage in our daily life. However, the first solution is the best one because of the necessity to re-use these products. Recently, researchers have been working on effective methods to dispose of these wastes by incorporating them in construction materials. The main objective of this project is to study how the properties of mortar could be affected by using crumb rubber as a partial replacement of fine aggregate. This experimental study is mainly aimed at analyzing the impact on the mortars compressive strength, flexural strength, and workability. Six mortar mixes were prepared with varying percentages of crumb rubber as partial replacement of sand (0%, 5%, 10%, 15%, 20%, and 25%). Sieve analysis for the crumb rubber and sand was performed. The surface of crumb rubber was not treated in order to explore how untreated tire particles could influence the mechanical properties of the mortar. Comparing the properties of mortar containing crumb rubber as partial replacement of sand to conventional mortar, it was found that the compressive strength, flexural strength, and workability decreased with the increasing percentage of crumb rubber. The mix with an imposing crumb rubber percentage that gave a combination of acceptable early and late strength (lightweight concrete) as well as acceptable flowability was found to be the one with 10% replacement, which will be considered the optimum mix.