Indian Concrete Journal

Strength and serviceability evaluation of steel fibre reinforced deep beams: A review Bijily Balakrishnan, Indu Geevar, Abins Aziz, Aysha Zeneeb Majeed

The applications of steel fibre reinforced concrete (SFRC) are limited in deep members, due to a lack of well-defined guidelines for design of such members. The present study evaluates the effect of steel fibres on strength, crack width and first shear cracking load using available experimental data on 127 SFRC deep beams with a shear span-to-depth ratio less than two. The study shows an average increase in strength and the first diagonal cracking load of 37 and 23 %, respectively for a fibre factor of 1. The data shows significant scatter, possibly due to inherent variability of SFRC. Nevertheless, SFRC deep beams are effective in crack control and exhibit good ductility response, and a reduction in distribution reinforcement is possible. The study also summarises the existing models for shear strength prediction of SFRC deep beams and three recent models are used for a comparative study. The study suggests strut-and-tie based model considering the contribution of fibres for design of SFRC deep beams

An experimental evaluation of service life for standard and highstrength self-compacting concrete incorporating sustainable and recycled construction materials B. Narendra Kumar, A. Meghanadha Reddy

In this study, an experimental investigation on self compacted concrete (SSC) was performed to obtain the properties such as, workability (slump flow, V-funnel and L box), mechanical strengths (compressive, split tensile and flexural strength) durability (half-cell potential, ultra sonic pulse velocity, chloride penetration depth and rapid chloride permeability test), and service life. Standard and high strength grades were developed by introducing the sustainable materials such as ground granulated blast furnace slag (GGBS) (fly ash-15 %), fine crushed rock aggregate (FCRA) (15 %) and FFA (50 and 100 replacements). Results were compared with a conventional mix wherein M-sand was used as fine aggregate material. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) were also used to analyse the microstructure of the concrete to understand its behaviour. The results reveal a lower strength, poor resistance to chloride attack and a lesser service life with higher fractions of recycled fine aggregate (RFA), although the effect was somewhat attenuated with low w/c ratio mixes. Up to 19 % strength decreased and at full replacement of aggregates 22.5 % strength decreased. About 100 % RFA, the standard grade has least durability. Service life has been predicted by simulation to be reduced by 45 % compared to the control concrete.

Fracture mechanics as the basis for structural design of fibre and textile reinforced concrete Ravindra Gettu

Fibre and textile reinforced concretes are composites with cementitious matrices and reinforcement in the form of discrete fibres or yarns. Since the matrices are brittle and defect sensitive, which may also be the case for some reinforcements such as glass and basalt, the behaviour is evidently governed by fracture mechanics. The review presented here discusses relevant developments, specifically at Indian Institute of Technology (IIT) Madras, related to these two materials with the objective of characterising them in a rational manner, so as to improve the performance and structural design. The main highlight of the work has been the development of testing methods and models to represent the post-crack response of the composite, such that this could be the input in the engineering of better materials and for structural design. Key research contributions arising from the work have been reviewed, including the use of interface finite elements to represent the cracking; development of a toughness test method that led to the IS: 17161, slab and pavement design methods, the inverse analysis procedure for determining the tensile constitutive relationship, fatigue and creep responses of fiber reinforced concrete; and the uniaxial tensile test method, including appropriate specimen fabrication and end conditions, the transition in the stress-strain response from softening to trilinear to bilinear, efficiency factors, size effects in the tensile response, durability criteria for design, and degradation mechanisms of textile reinforced concrete. For both types of composites, pilot projects, mostly novel in the Indian context, have been undertaken based on the research outcomes, with many of these currently being in service on the IIT Madras campus.

Strength characteristics and acid resistance of pumice lightweight aggregate concrete: A microstructural perspective Chaitali B. Guledagudd, Kannam Praveen

Lightweight concrete (LWC) is a pioneering solution in the construction sector, characterized by its unique composition and versatile applications. Engineered with lightweight aggregates and additives, LWC achieves a significant reduction in dry density, making it 23 to 87 % lighter than conventional concrete. Pumice stone, a volcanic rock, is often chosen as a replacement for coarse aggregate due to its natural lightness and porous nature, which can improve thermal insulation properties. This study investigates the optimal dosage of pumice lightweight aggregate in LWC production, focusing on 28 day compressive strength. The results show that a 40 % pumice lightweight aggregate replacement level is optimal for M30 and M50 grade concrete, with improved compressive strength, split tensile strength, and modulus of rupture. Durability assessment of 40 % pumice-replaced concrete under 5 % sulphuric acid, chosen for its severity, showed acceptable strength and microstructural performance. Future work can include tests like chloride penetration, carbonation, and freeze-thaw for broader evaluation. Microstructural analysis using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD) confirm the suitability of pumice aggregate as a percentage replacement for normal coarse aggregate in producing structural lightweight aggregate concrete.

Long-term durability of ambient cured fly ash based geopolymer concrete by acid attack and sulphate attack Bhushan H. Shinde, Bhagyashri S. Nawale, Kshitija Kadam, Sunil B. Somani

The fly ash based geopolymer concrete with temperature curing and ambient curing has been prepared with four different strength. For ambient curing, only 4 % of ordinary Portland cement is used to replace fly ash in order to gain strength at ambient temperature. For comparing the results the conventional cement concrete has been prepared of similar compressive strengths of geopolymer concrete with temperature concrete (GPCT). All the mixes has been prepared with 45 % river sand plus 55 % treated sea sand as a fine aggregate. To evaluate long-term durability, acid attack and sulphate attack tests are conducted for the exposure periods of 1, 4, 8, 12, 24, 36, and 52 weeks. Durability is evaluated in terms of weight loss and compressive strength of the specimens. A total of 504 cubes are cast under 12 different mix combinations. The results show that geopolymer concrete cured at elevated temperatures and geopolymer concrete cured at ambient temperatures offer greater resistance to acid attack and sulphate attack, compared to cement concrete.