Indian Concrete Journal

Retrofitting of reinforced concrete box culvert using fiber reinforced polymer composites - a numerical investigation Vaibhav Dhiman, Swati Maitra

Reinforced concrete box culverts are subjected to moving loads and weathering actions which results into faster deterioration mainly in the form of cracking/spalling of concrete leading to corrosion of reinforcements. Corrosion causes loss of materials which reduces the service life. Retrofitting a deteriorated box culvert with fiber reinforced polymer (FRP) composites can effectively enhance its performance and durability. In the present work, a three-dimensional finite element model has been developed for a typical box culvert and different levels of deterioration along with a retrofitting strategy with FRP have been simulated. The analysis shows a significant improvement in performance of the retrofitted box culvert.

Development of various characteristics and fracture mechanism of high strength concrete at optimum content of supplementary cementing materials and steel fibers polymer tendons Jagdish Chand, S. M. Gupta, Babita Saini

The high strength concrete has been found brittle in nature due to smooth failure plane between the closely packed dense matrix of aggregates and cement paste; results in sudden failure of the structure. Investigation through the literature data provides considerable variation in the mechanical properties of it, containing part replacement of cement with supplementary cementing materials (SCM) and various proportions of steel fibers. More research and results are required to evaluate the function of SCM and steel fibers for the development of different characteristic of high strength concrete. The present paper contributes a part of current investigations made through experimental laboratory work to evaluate the mechanical and shear properties of high strength steel fiber reinforced concrete (SFRC). Parametric variations of silica fume from 5 to 15% and fly ash 30% have been used as replacement of cement to ascertain the properties of concrete. The quantity of steel fibers varies from 0.5 to 2% with 0.5% increment was used in the experimental study. Besides for comparison, one mix named controlled mix was produced without silica fume contents and steel fibers. The prime objective includes determining the optimum SCM content by progression of laboratory experiments for the most favorable mix proportions of high strength SFRC. An average slump loss for all the three mixes has been found as 78% from 0 to 2% steel fiber volume corresponding to 12% silica fume, 1.5% steel fiber volume and 30% fly ash. The strength ratio development from 7 to 56 days of high strength SFRC has been found as 0.85 whereas the same was found as 0.65 corresponding to control concrete. This is perhaps due to the reason that silica fume improves the performance of high strength SFRC at early age and the pozzolanic material present in the fly ash react with residual lime and improve the characteristics of high strength concrete at later stage. The addition of silica fume with fly ash was found to increase the compressive strength of concrete at early age when compared to concrete made with fly ash alone.

Experimental study on creep and shrinkage behavior of high strength concrete for application in high rise buildings P. N. Ojha, Brijesh Singh, Abhishek Singh, Vikas Patel, V. V. Arora

A concrete structure when subjected to sustained load presents progressive strain over time, which is associated with the creep phenomenon. An experimental study was conducted to determine the time induced creep strain of high strength concrete using creep rig of capacity 2000 kN. Creep strains are measured at regular time intervals on concrete designed with water to cementitious ratio of 0.47 and 0.20 wherein fly ash and silica fume were also used. In the current study, the experimentally measured values of creep are presented for concrete strength of about 45 MPa and 100 MPa. The experimentally obtained creep and shrinkage strain values are compared with B-3 Model, International Federation for Structural Concrete (FIB) model code 2010 and B4 model. The paper also presents the comparison of creep coefficients obtained using the above mentioned models with the values currently existing in Indian Standard IS: 456 (2000) and highlights the needs for the revision in creep coefficient in Indian Standard. The creep coefficients determined using B3 and B4 model are over estimating the values in case of high grade concrete. The creep coefficients determined using FIB model code 2010 are closer to IS: 456 (2000) values. The primary reason for over estimation of creep in high strength concrete using B3 and B4 model can be attributed to chemical volume reduction and self-desiccation along with decrease in pore humidity. The complications arise in creep prediction while using B3 and B4 model due to attenuating effects of diverse admixtures and reactive additives present in high strength concrete. In FIB model code 2010, basic creep concept has been used. Wherein, basic creep has been modelled using a logarithm function, which is infinite ongoing deformation while drying creep approaches a finite value. The creep given by FIB model code 2010 is similar to shrinkage modelling and this is one of the key factors contributing to accurate estimation of delayed deformations in high strength concrete. In the case of high strength concrete, IS: 456 (2000) creep coefficients will not hold good and needs to be revised. The FIB model code 2010 empirical equations can be adopted for the revision of IS: 456 (2000) which gives reasonably closer values to the experimental creep co-efficient compared up to 180 days of loading.

Conceiving of extradosed bridges V. N. Heggade

The Indian designers and contractors preferred long span concrete girder bridges constructed by cantilever method of construction to span rivers, strait crossings, ravines and gorges, for overcoming the foundation problems and to provide navigational clearance, etc. Barak Bridge at Silchar built in 1961 was first of this kind constructed by cantilever cast-in-situ segmental construction method in India. Since then many cantilever girder bridges using cast-in-situ or precast segmental technology have been constructed, the longest span being 165 m. The design and construction technology warranted for extradosed bridges is akin to cantilever bridges. Thus for having perfected the technology over the period, it was an organic choice for Indian designers to go for extradosed bridges which has a striking similarity to that of cable stay bridges.

Hence, there is a spurt of burgeoning of Extradosed bridges in the country due to its innate design and construction friendly nature. Siddapur bridge at Coorg in Karnataka is the first indigenously designed and constructed by cast-in-situ cantilever construction method extradosed bridge in India. At the same time Indraprastha, Moolchand bridges by DMRC and 2nd Vivekananda bridge at Kolkata which were designed by expat consultants & realized by pre-cast segmental construction technology were under construction.

Logically, the organic evolution of cable supported bridges should have been in the order of girder bridges to suspension bridges or otherway round. But in reality, the suspension bridges gave rise to cable stay bridges and cantilever girder bridges was conceptually was extrapolated to extradosed bridge despite its striking visual similarity with cable stay bridges.

Flexural behavior of reinforced cement concrete beams made with air-cooled ferrochrome slag coarse aggregate Prasanna Kumar Acharya, Sanjaya Kumar Patro

This paper manifests on the potential use of air-cooled ferrochrome slag (ACFS) as a coarse aggregate of structural concrete. The construction industry is the greatest consumer of natural materials. Due to the rapid depletion of non- renewable natural resources, scientists around the globe are trying hard to find out suitable local alternatives to virgin materials. Industrial waste materials are reported as the best alternatives and ACFS is one of them, which possesses all desired engineering characteristics of coarse aggregate used in concrete. The physical, chemical and mechanical properties of ACFS were studied and found better to those of natural coarse aggregate. The flexural characteristics of reinforced concrete beams made with natural coarse aggregate and ACFS coarse aggregate were compared and it was observed that the latter has supremacy over the former.