Experimental Investigation on Plain and Reinforced Fibre Based No-Aggregate Concrete

Abstract

Developing countries like India are witnessing the infrastructure growth which is at its peak level. This ultimately leads to increase in demand of construction materials. Of all the construction materials, demand for cement is costliest and energy intensive component of concrete. Manufacturing of cement discharges significant amount of carbon-dioxide in the atmosphere. It also consumes large part of limestone which is available in a limited quantity. Fly ash which is the major by-product of all the thermal power stations need to be dumped which adds to the cost. Leading towards the greener world, many cement manufacturers have started using y ash in manufacturing cement. The reduction of the cement content in the concrete will pose difficulty in achieving the desired strength. So, to overcome this type of problem requires such material which can replace cement without any loss in strength. One of the numerous contrasting options to deliver environmental friendly concrete is to supplant the measure of portland bond in cement by y ash. Here comes a new type of material known as No-Aggregate Concrete (NAC). It is devoid of aggregates, neither coarse nor fine. It is initiated by Institute for Solid Waste Research & Ecological Balance (INSWAREB), Visakhapatnam. The NAC is devoid of fine and coarse aggregates but having the engineering properties compatible to a structural concrete in addition to high strengths. NAC contains low cement (OPC) content of 300-320 kg/m3, but rendering grade strength of 50-80 MPa. In this concrete, y ash contributes to 75% of cementitious materials and remaining 25% is of cement. This type of concrete has very good ow-ability characteristics. It is cheaper compared to control concrete because y ash is the major constituent which is available at cheaper price and also as aggregates are not used for its preparation. So, focus of the present investigation is to explore the properties of No-aggregate concrete. No-aggregate concrete has high compressive strength which leads to its brittle failure without giving any warning. It suddenly ruptures and burst under bending loads. To arrest the propagation of cracks and sudden failure, use of different types of fibres is attempted to check the improvement in properties of no-aggregate concrete. Therefore, main objectives of study is to check the performance of NAC by adding different types of fibres like steel fibres with hooked ends, polypropylene fibres and hybrid fibres. Properties of No-aggregate concrete with fibre of four different categories such as NAC, NAC with polypropylene fibres (NACPF), NAC with steel fibres (NACSF) and NAC with hybrid fibres (NACHF) are compared in the present investigation. Different mechanical & durability properties such as compressive strength, exure strength, split tensile strength, modulus of elasticity, impact energy, abrasion resistance, bond strength, sulphate resistance, chloride resistance and acid resistance are evaluated for all four concrete mixes for PCC elements. Test result demonstrates that due to the incorporation of fibres in the concrete mixes, enhancement for all mechanical properties have been observed for NACPF, NACSF and NACHF mixes as compared to that of NAC. Major improvement has been observed in

exure strength, split tensile strength, impact energy and abrasion resistance. Results of concrete mix with fibres for compressive strength, modulus of elasticity and bond strength are observed to be at par to that of NAC mix. Test results have indicated that NAC and NAC mixes with fibre posses good durability properties. Minimal reduction in weight and compressive strength has been observed for all NAC mixes as compared to that of CC during acid resistance test. Good resistance of all NAC mixes during sulphate resistance test and chloride resistance test has been observed. This shows the superior performance of NAC mixes as compared to that of CC. Total 10 RC columns of five categories such as control concrete (CC), NAC, NACPF, NACSF & NACHF having cross sectional dimensions 150 mm 150 mm and height of 1 m are cast. The columns are having the same percentage of reinforcement and same cement content. For each category of RC column, two columns are tested and their aver- age results are considered for the final result. The experimental results of ultimate failure load, de ection, stress-strain, failure modes & crack patterns have been obtained and compared for all RC columns. Test results for RCC element demonstrated that due to the incorporation of fibres in the NAC mixes, there is minor improvement in ultimate load carrying capacity but the de ec- tion and strain increases significantly as compared to that of NAC. Also, with such low cement content of 320 kg/m3, reinforced CC column is able to achieve average ultimate load capacity of 375 kN whereas, NAC mixes are able to achieve ultimate load carrying capacity in the range of 768 kN to 883 kN. Fibres prevented the early spalling of concrete which resulted in higher axial load carrying capacity for NAC mixes with fibres. Fibres impart the ductility and prevents the brittle failure & bursting effects in RC elements for NAC mixes with fibres.