Use of Fibre to Address the Brittleness of No Aggregate Concrete

Abstract

Concrete is second largest material used in the world. Due to the development of infrastructure, the use of cement and aggregate has been signi cantly increased. For the production of 1 tonne of cement, 1 tonne of CO2 is released in the at- mosphere. Cement uses a large amount of limestone, which a natural resources available in a limited quantity. It is very much essential to nd an alternative to limestone, which is cheep and also it will help to solve the above issue. Many waste products are available in market, which is used in concrete such as y ash, silica fume, slag, etc. But out of that y ash is one of the product which is available easily. Fly ash is the by-product of thermal power plant. After processing the y ash can be used as a cementitious material in concrete. Use of y ash has been arrived due to limited natural material resources for the manufacturing of cement. Generally, 20-30 % y ash is replaced with cement in concrete manufacturing. A new type of concrete is proposed here which is made without use of aggregate and by replacing major amount of cement by y ash. The name of this concrete is "No-Aggregate Concrete (NAC)" which has been innovated by Dr. N Bhanu- mathidas and Mr. N Kalidas [1][2]. In NAC, all types of aggregates are removed and bulk amount of cement is replaced with Class F y ash. The cement and y ash used in NAC are in proportion of 1:4. NAC has high compressive strength but due to brittleness in nature, NAC shows sudden cracks. It suddenly ruptures and burst under bending. Therefore, the bre is added in NAC. Steel hook ended bre is used in this investigation. The length and diameter of bre are 60 mm and 0.75 mm, respectively. The complete matrix of NAC and bre are called as "No-Aggregate Concrete with Fibre (NACF). The main aim of the study is to use the bre in NAC to improve ductility of NAC. Experimental investigation is conducted on four di erent concrete mixes such as No-Aggregate Concrete with Fibre (NACF), No-Aggregate Concrete (NAC), Con- trol Concrete (CC) & Control Concrete with Fibre (CCF). Di erent mechanical properties such as compressive strength, split tensile strength, exural strength, modulus of elasticity, impact energy and abrasion resistance are evaluated for four concrete mixes. Mechanical properties such as compressive strength, split tensile strength, exural strength and modulus of elasticity are evaluated at 7, 28 and 90 days for all concrete mixes. Impact energy and abrasion resistance properties are evaluated all concrete mixes at 28-days. Total twelve RC beams of all four categories such as NAC, NACF, CC & CCF having cross sectional dimensions 150 mm x 200 mm with an e ective span of 1.1 m are cast with the same percentage reinforcement. In each category of RC beam, three beams are tested and there average results are considered. The experimental results of failure loads, de ection, strain, moment capacity and crack pattern have been observed and compared for all RC beams. Test results demonstrate that due the incorporation of bres, improvement in all mechanical properties have been observed in NACF and CCF mixes compared to NAC and CC mixes, respectively. At 28-days, compressive strength of NACF and CCF mixes are 5.57% and 14.08% higher as compared to NAC and CC mixes, respectively. A 28-days, exural strength of NACF and CCF mixes is 52.68% and 53.47% higher as compared to NAC and CC mixes, respectively. At 28-days, split tensile strength of NACF and CCF mixes is 41.58% and 42.01% higher as com- pared to NAC and CC mixes, respectively. At 28-days, Modulus of Elasticity of NACF and CCF mixes is 10.49% and 5.18% higher as compared to NAC and CC mixes, respectively. At 28-days, impact energy at ultimate failure load of NACF and CCF specimens is 99.14% and 94.67% higher as compared to NAC and CC specimens, respectively. At 28-days, for abrasion resistance test percentage weight loss at 500 r.p.m. of NACF and CCF specimens are 1.94% and 31.67% lower as compared to NAC and CC specimens, respectively. In case of abrasion resistance test at 500 r.p.m., there is a minor weight loss for CCF specimens as compared to CC specimens. But, there is signi cant weight loss in NAC as compared to NACF specimens. The results related to di erent properties of RC beam elements such as ultimate load carrying capacity, moment carrying capacity, de ection & strain have sug- gested that due to the addition of bre, all properties of RC beam elements are improved. Due to the addition of bre, the experimental value of load carrying capacity at ultimate load of NACF and CCF mixes are 7.78% and 16.38% higher than NAC and CC mixes, respectively. The experimental value of de ection at ultimate load of NACF and CCF mixes are 19.82% and 7.41% higher than NAC and CC mixes, respectively. NACF, CC & CCF RC beams fail in exural but NAC RC beams fail in shear at ultimate load. All experimental values of di erent properties are higher than the theoretical values. From results of mechanical properties of PCC elements, it has been observed that due to incorporation of bre, there is a minor improvement in compressive strength, Modulus of Elasticity of NACF and CCF mixes compared to NAC and CC mixes, respectively. But, there is a major improvement in exural strength, split tensile strength & impact energy of NACF and CCF mixes compared to NAC and CC mixes, respectively. All mechanical properties except abrasion resistance of PCC elements of NAC and NACF are higher compared to CC and CCF. Due to incor- poration of bre, there is a minor improvement in ultimate load carrying capacity and moment carrying capacity of RC beams in NACF and CCF mixes compared to NAC and CC, respectively. All concrete mix RC beams except NAC RC beams fail in exural for same reinforcement.