STRUCTURAL PERFORMANCE OF SISAL FIBERS REINFORCED LIGHTWEIGHT CONCRETE WITH WASTE PLASTIC PRE-COATED VOLCANIC SCORIA AGGREGATES.

Abstract

Concrete is by far the most common material used for construction purposes all around the world. Structural Lightweight Concrete (SLWC) is a specific type of Lightweight Concrete (LWC) developed when there is need to produce both a strong and light concrete having other specific properties such as insulation (thermal, sound). However, instead of the use of Artificial Lightweight Aggregates (ALWA) such as expanded shales, clay and slates commonly used, this study investigated the use of Natural Lightweight Aggregates (NLWA) such as volcanic scoria for producing SLWC. ALWA are known for high carbon emission and high energy consumption in the manufacturing process which make them costly and environmentally dangerous. Previous studies on volcanic scoria aggregates used in concrete have revealed relatively weak mechanical and physical properties mainly due to its high degree of porosity leading to a high water absorption capacity in concrete and therefore low strengths. To address the issue, waste plastics (WP) were used in this study to pre-coat them in a hot mix process in order to reduce their pores before using them to produce SLWC reinforced with natural sisal fibers (NSF). The aim of this research was to produce a relatively strong SLWC, using NLWA such as volcanic scoria and NSF in the matrix, while disposing the waste plastics from the environment. A SLWC with uncoated volcanic scoria aggregates, having no fibers in the matrix was designed as the control mix, following the specific steps prescribed by ACI 211.2 Standard, with 30 MPa as the design strength. Then, three main phases were adopted. (i) Investigation of the effects of WP over the aggregates on the SLWC properties. Three LWC specimens were produced with waste plastic pre-coated scoria aggregates at 5%, xxi 10% and 15% by weight replacement of aggregates in a hot mix process. It was noticed a great influence of WP over the aggregates on the LWC properties. The best WP content was found to be 5%. The 28 days compressive strength, splitting tensile strength and flexural strength were found to increase by 10.46%, 1.82% and 3.43% respectively as compared to the control. (ii) Determination of the influence of addition of NSF in the concrete matrix on the LWC properties. Three different short discrete fibers contents (1%, 1.5%, and 2%) of length 3 to 4 cm by weight of cement, were used in the matrix of LWC mixes containing waste plastic pre-coated volcanic scoria aggregates at 5%. The results showed that the best NSF content was 1%. With comparison to the control, the 28 days compressive strength decreased by 25.49% while the 28 days splitting tensile strength and flexural strength increased by 6.20% and 40.81% respectively. (iii) Assessment of durability performances and Comparison of the structural responses of the two main specimens under the study, the control mix named S0 and the LWC made with waste plastic pre-coated volcanic scoria aggregates at 5%, having 1% of NSF in the matrix named S1. The results showed a better resistance to chloride penetration of S1 mix specimens as compared to the control mix S0. Three steel-reinforced beams of 150 x 200 x 1000 mm of each specimen were casted and tested under bending. S1 beam specimens were found structurally more efficient than S0 beam specimens. S1 beams showed better ability to sustain more loads with higher failure strains. This was due to NSF which controlled cracks and acted as cracks arresters. S1 beam specimens was found more ductile than S0 beam specimens.