The demand of concrete is increasing day by day for satisfying the need of development of infrastructure facilities. It is well established fact that the production of OPC not only consumes significant amount of natural resources and energy but also releases substantial quantity of carbon dioxide to the atmosphere. Therefore, it is essential to find alternatives to make the concrete environment friendly. Geopolymer is an inorganic alumino-silicate compound, synthesized from fly ash. The fly ash, one of the source materials for geopolymer binders, is available abundantly in India, but to date its utilization is limited. Hence it is essential to make the efforts to utilize this by-product in concrete manufacturing in order to make the concrete more environmental friendly. This paper describes the experimental work conducted by casting 20 geopolymer concrete mixes to evaluate the effect of various parameters affecting its the compressive strength in order to enhance its overall performance. Various parameters i.e. ratio of alkaline liquid to fly ash, concentration of sodium hydroxide, ratio of sodium silicate to sodium hydroxide, curing time, curing temperature, dosage of superplasticiser, rest period and additional water content in the mix have been investigated. The test results show that compressive strength increases with increase in the curing time, curing temperature, rest period, concentration of sodium hydroxide solution and decreases with increase in the ratio of water to geopolymer solids by mass & admixture dosage, respectively. The addition of naphthalene based superplasticiser improves the workability of fresh geopolymer concrete. It was further observed that the water content in the geopolymer concrete mix plays significant role in achieving the desired compressive strength

In recent years, the use of externally bonded fiber-reinforced polymers (FRP) has become increasingly popular for civil infrastructure applications. The Glass fiber reinforced polymer has significantly enhanced the strength and ductility of concrete by forming perfect adhesive bond between concrete and the wrapping material. Present experimental investigation mainly emphasises on effectiveness of external GFRP strengthening for RC Columns of circular, square and rectangular shapes having same cross sectional area. Total 15 RC columns of 1 meter in height were cast. 9 columns were control and the rest 6 columns were strengthened with one layer of GFRP wrap having 20mm of corner radius. Columns were designed using IS: 456:2000 provisions. Design of GFRP wrapping was done using ACI 440.2R.08 provisions. All the test specimens were loaded to fail in axial compression and strain of the columns in the axial direction was investigated. The test results clearly demonstrated that the axial load carrying capacity increases from rectangular to square to circular shape of confined RC columns. No major impact on axial compressive strength is observed due to variation in shape for control columns, on the other hand, quite opposite behaviour was observed in case of RC columns confined by GFRP. GFRP wrapped circular column undergone more axial deformation as compared to that of square and rectangular columns. Stress-strain behaviour revealed that the strength gained from FRP confinement was prominent for circular columns. Square and rectangular-section columns are found to experience lesser increment in strength as compared to that of circular columns. This behaviour may be attributed to variation in lateral confining pressure distribution for rectangular columns from a maximum at the corners to a minimum in between, which is in contrast to even confining pressure observed for circular columns in order to achieve the full confinement effect

Strengthening of Reinforced Concrete (RC) beams is required due to design errors, deficient concrete production, bad execution processes, damage due to earthquake, accidents such as collisions, fire, explosions and situations involving changes in the functionality of the structure etc. Jacketing has been considered as one of the important methods for strengthening and repairing of RC beams. Jacketing of RC beams is done by enlarging the existing cross section with a new layer of concrete that is reinforced with both longitudinal and transverse reinforcement. In the present investigation, 10 beams of size 150mm x 300mm x 2100mm are cast. 4 RC beams are prepared with smooth surface; on the other hand, 4 RC beams are prepared with chipped surface. Remaining two RC beams are considered as control beams. Eight RC beams have been jacketed using additional reinforcement for 60mm thickness all-round. Four different methods have been employed for jacketing of RC beams. These methods include use of dowel connectors and micro-concrete, bonding agent and micro-concrete, combined use of dowel connectors, bonding agent and micro-concrete and use of only micro-concrete without dowel connectors and bonding agent, respectively. After 28 days of curing period and completion of jacketing process, these RC beams are tested under two point loading system. Measurements taken during testing were central displacement, failure load, and failure mode & crack patterns. Effectiveness of each type of jacketing methodology on smooth surface was compared with chipped surface for the RC beams. As an outcome of investigation, for smooth surface RC beam, superior performance was observed for the beam jacketed using combined dowel connectors and bonding agent with micro-concrete. For chipped surface RC beams, superior performance was observed for the beam jacketed using only micro-concrete and without use of dowel connectors and bonding agent

This paper evaluates the properties and use of recycled rubber tyres in the form of rubber crumb as a freeze/thaw protection agent when used in concrete. Reusing scrap tyres in the form of rubber crumb in concrete could benefit the environment by contributing to the percentage of tyres used for a variety of recycling processes such as carpet underlay or tyre derived fuel, thus reducing disposal of tyres to landfill sites and the chemical usage of air entraining agents as a means of achieving freeze/thaw protection. Concrete cubes of 100mm were produced from design mixes which have been classified as plain, air entrained and rubber crumb and subjected to freeze/thaw cycles at 5 days of age. Thawing was conducted in water to ensure full saturation of pores and maximum stress on the concrete samples. The rubber crumb and plain concrete mixes were compared against the freeze/thaw performance of that entrained with air. Air entrainment is known to protect against freeze/thaw action. Rubber crumb when ...

Existing reinforced concrete (RC) columns may be structurally deficient due to variety of reasons such as improper transverse reinforcement, flaws in structural design, insufficient load carrying capacity, etc. Carbon/Glass fibre reinforced polymer (FRP) confinement can be effectively used for strengthening the deficient RC columns. The effectiveness of FRP wrapping for RC columns mainly depend upon corner radius of the specimens as well as number of FRP layers used for the confinement. An attempt has been made hereby to investigate the experimental behaviour of GFRP wrapped small scale square RC columns with varying corner radii. Experimentally evaluated behaviour of GFRP wrapped RC columns is compared with the performance observed for non-wrapped RC columns. 15 RC columns having cross-sectional dimensions 125mm × 125mm and length of 1200mm have been tested under axial compression. Three columns are unwrapped and have been designated as control specimens. Three columns each with corner radius equivalent to cover of 25mm are wrapped with one and two layers of GFRP, respectively. To avoid a premature rupture of the GFRP composite, remaining six columns with corner radius of 5mm have been wrapped with one and two layers of GFRP, respectively. GFRP wrapped columns go under higher axial displacement in order to gain higher compressive strength over the control column. The results showed that smoothening of the edges of square cross-section of RC columns play a significant role in delaying the rupture of the FRP composite at the edges. Corner radius equal to concrete cover gives better results in terms of ultimate load carrying capacity than the corner radius less than cover for confined RC columns