Author: Zhang, Binyu
Title: Eco-friendly construction materials prepared with light weight and rubberised concrete
Degree: Ph.D.
Year: 2017
Subject: Hong Kong Polytechnic University -- Dissertations
Lightweight concrete
Aggregates (Building materials)
Concrete -- Environmental aspects
Pages: xvi, 132 pages : color illustrations
Language: English
Abstract: In this thesis, experimental tests were focused on improving thermal insulation properties and acoustic insulation properties of lightweight aggregate concrete with recycled aggregate incorporation. In the first part, Furnace Bottom Ash (FBA) was used to replace natural fine aggregate. The experimental results demonstrated that, the lightweight aggregate used in this study improved concrete thermal insulation properties of concrete compared to natural aggregate, and with the incorporation of FBA, the thermal conductivity of lightweight aggregate concrete was further reduced. The reduced thermal conductivity enhances the sustainability of the material. The mechanical properties evaluation showed that the incorporation of both lightweight aggregate concrete and high volume of FBA led to strength loss and stiffness loss, the use of silica fume showed limited effect on strength loss compensation. However, with high volume of FBA incorporation, the lightweight aggregate concrete still met the minimum strength of structural lightweight aggregate concrete. The feasibility of high volume FBA incorporation is of great importance for industrial by-product’s recycling and reusing. Lightweight aggregate and FBA incorporation resulted in poor durability properties of concrete indicated by the results of the chloride ion penetration test. High permeability of lightweight aggregate concrete is associated with high maintenance cost. In this study, silica fume was added to FBA incorporated lightweight aggregate concrete to compensate the strength loss as well as to improve the impermeability of concrete. Furthermore, the internal curing effect has been studied. FBA and the lightweight aggregate are porous aggregates, pre-wetting was conducted before casting. The shrinkage tests showed that the incorporation of pre-wetted lightweight aggregate resulted in reduced autogenous shrinkage which was attributed to the internal curing effect of the aggregate, and the incorporation of FBA further reduced concrete’s autogenous shrinkage. In the first part, the feasibility of using high volume industrial by-product to fabricate structural lightweight aggregate concrete with improved thermal insulation properties has been proven. In the second part, recycled rubber aggregate made from waste tires was added into concrete to partially replace FBA and to replace natural fine aggregate. The noise attenuation test was conducted and the results showed that the incorporation of recycled rubber aggregate has a positive effect on noise reduction effect of concrete slabs. Within the frequencies range 100Hz to 3150Hz, increased rubber content led to enhanced overall noise reduction of rubberised concrete.
Segregation and poor consistency were observed when high volume of rubber aggregate was added. Various surface treatment methods had been applied to modify the rubber aggregate’s surface. Chemical modification was applied by the immersion of rubber aggregate in saturated sodium hydroxide solution and in Silane Coupling Agent (SCA) solution. However, the mechanical properties test showed that the chemical modification caused slightly strength loss, and no difference was detected at the noise attenuation test comparing the specimens containing 50% as-received rubber aggregate and 50% chemical treated rubber aggregate. When a simple cement paste coating pre-treatment method applied to modify the rubber aggregate surface, acoustic insulation properties of rubberised concrete was further improved. Then the dynamic Young’s modulus of the rubberised concrete with as-received rubber aggregate and with cement paste coated rubber aggregate has been tested. The results showed that the specimens that contained pre-treated rubber aggregate had a lower dynamic Young’s modulus compared to the specimens with same amount of as-received rubber aggregate. The bonding strength test results illustrated that when the cement paste coating was applied, the bonding between rubber aggregate and the matrix became weaker. In the second part, the use of high volume rubber aggregate to produce lightweight aggregate concrete with improved sound insulation properties has been investigated, the rubber aggregate surface modification method was found to further improved noise reduction effect of specimens. The mechanism has been proposed: cement paste coating on rubber aggregate resulted in a weaker bonding and a decreased dynamic young’s modulus, thus upon vibration the specimen with pre-treated aggregate absorbs energy more quickly and easily, and consequently this pre-treatment method leads to enhanced noise attenuation capacity of rubberised concrete.
Access: open access

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