The first paper, “Behavior of Exterior Beam-Column Joints Reinforced Internally with Threaded GFRP Reinforcements”, by Saravanan Jagadeesan and Kumaran G, focuses on the study of behavior of exterior beam-column joint reinforced with GFRP reinforcing bars. The joints were cast and tested under uniform axial compression and uniaxial bending applications. The authors have also tested two different kinds of joints, one with stirrups and another without stirrups. This has been done with an aim to reduce or eliminate the use of conventional bars as construction materials. In the testing phase, constant axial compressive load was applied on column and beam was subjected to increasing monotonic loading. It was observed in most of the joints that first crack developed in the beam or near the beam-column joint interface. It was noticed in both steel reinforced and GFRP reinforced test specimens. Three-dimensional eight-noded solid isoparametric element has been used to model concrete. It allows plastic deformations, cracking in three orthogonal directions and crushing also. The results obtained from experiments and analytic work have been compared and it is found that results are identical for both the specimens reinforced with steel and GFRP. The failure pattern observed experimentally is also found to be exactly similar to the cracking pattern observed from the ANSYS 10 program. The authors conclude that the behavior of beam-column joints reinforced with GFRP reinforcements is too complex to be exactly represented by the simple strut and tie model as used in the study and also reported in existing theories.

The focus of the second paper, “Study on the Strength Characteristics of SCC with GGBS and RHA as Mineral Admixtures”, by M Swaroopa Rani, K Jagannadha Rao and M V Seshagiri Rao, is to achieve a durable concrete with the use of Self-Compacting Concrete (SCC). The use of steel is also increasing, leading to difficulties in compaction of concrete during construction. To overcome this problem of compaction, SCC was introduced, which facilitates the construction as well as reduces the time of construction to some extent. The authors have investigated the behavior of fresh and hardened properties of concrete of SCC grade with M20, M40 and M60 strength. Further, Ground Granulated Blast Furnace Slag (GGBS) and Rice Husk Ash (RHA) have been added to the mix for concrete and its strength observed. In the study, SCC mix uses cement, fine and coarse aggregate water, mineral admixtures like GGBS, RHA, superplasticizers and Viscosity Modifying Agent (VMA). The benefits received in using GGBS are lower heat of hydration, reduced permeability, resistance to sulphate attack, resistance to chloride attack and resistance to alkali aggregate reaction. VMA increases cohesive property of SCC without altering its fluidity and is a stabilizing factor in concrete mixture. The results obtained indicate that workability of SCC mix increases with increasing percentage of GGBS in all grades of concrete. The SCC mix with GGBS as partial replacement of cement shows lower strength at early age. The study indicates that GGBS and RHA can be used for different grades of SCC without compromising the strength.

The focus of the third paper, “Durability of Fly Ash Concrete to Chloride Ingress”, by Thilgavathi S, Dhinakaran G and Venkataramana J, is to study the behavior of chloride ion ingress in the Fly Ash (FA) mixed concrete. The study focuses on the performance of concrete with different proportions of FA as a permeability reducing admixture. The economic and ecological benefits of use of FA in concrete improves strength and enhances the chloride resistance. In this work, the authors have used concrete of strength 40 N/mm2 with and without mineral admixture and different water/cement (w/c) ratios such as 0.32, 0.35, 0.4 and 0.50. Further FA has been used as a mineral admixture to assess its influence on the compressive strength and chloride resistance of concrete for various curing periods. Chloride resistance experiment has been performed using Rapid Chloride Permeability Test (RCPT) setup, as prescribed in ASTMC1202 recommendations. The results indicate increase in the strength of FA mixed concrete than normal concrete at lower w/c ratio. The variation of voltage causes significant changes in control concrete than FA mixed concrete. It shows that the effect of voltage plays a vital role in the concrete with moderate w/c ratios and advises that RCPT is not suitable below 30 V. Addition of FA does not adversely affect alkalinity of the concrete, which will be helpful for maintaining the steel in a passive state itself.

The fourth paper, “Cement and Polymer-Based Concrete Composites for Retrofitting of Structures”, by Balamuralikrishnan R and Antony Jeyasehar C, focuses on the results obtained by retrofitting of structures using cement and polymer-based composites. The authors report the results of experimental and analytical studies on the flexural strength of RC Beams, using externally bonded composites like Slurry Infiltrated Mat CONcrete (SIMCON) laminates and also polymer-based composites like Carbon Fiber Reinforced Polymer (CFRP) laminates. SIMCON laminate use can enhance flexural strength by as much as 45% for laminates having volume fraction 5.5% and aspect ratio 300 and 400. The flexure strength increases substantially up to 89% for volume fraction 5.5% and aspect ratio 400, and even 100% with volume fraction 5.5% and aspect ratio 300. At ultimate load level of controlled specimen, the strengthened beam shows a decrease of deflection up to 87%. Beams strengthened with SIMCON experience flexural failure, and none of the test specimens exhibited premature brittle failure. Beams strengthened with CFRP fabric exhibited increase in flexural strength up to 18 to 20% only. This beam also undergoes flexural failure and no premature brittle failure. The study concludes that use of SIMCON for retrofitting of concrete beams and columns is a better option than CFRP fabric for strength enhancement of structures. The cost factor also has to be watched.

-- Satyendra P Gupta
Consulting Editor