Indian Concrete Journal

Simplified modelling approach for predicting lateral load behavior of GFRG walls Gouri Krishna S. R., Devdas Menon, Meher Prasad A.

Glass Fibre Reinforced Gypsum (GFRG) panels are used as walls and slabs with Reinforced Concrete (RC) infilled in their cavities. The behavior prediction of RC infilled GFRG walls under lateral load requires proper modelling techniques. In the present study, a simplified analytical model is proposed for the estimation of lateral load-displacement behavior of GFRG walls with RC infill. The model uses the moment-curvature relations developed using the proposed algorithm assuming linear strain variation along the width of the wall. The effect of interfacial slip is also accounted for in the present formulation by applying a correction factor to initial stiffness. The predicted values showed reasonable match when compared with experimental results.

Shear strength and rationality of strut-and-tie method for design of deep beams Appa Rao G., Kondalraj R.

The shear span-to-depth ratio (a/d) is the most important factor influencing the shear strength of reinforced concrete beam and makes the failure mechanism a complex one. As the a/d ratio decreases, the shear strength of beam increases, by altering the mode of failure from diagonal tension to diagonal compression. IS: 456 (2000) and Euro code 2 developed shear strength expression empirically from the experimental results of beams with a/d ratio of more than 2.0, and the same has been adopted with an enhancement factor for the design of beams with a/d ratio of less than 2.0, ignoring the mode of failure. The validity of these modified expressions has been reviewed using experimental database of 227 beam test results with a/d ratio of less than 2.0. In addition, the ACI 318-14 provisions based on the strut-and-tie model (STM) have been reviewed. The STM based approach seems to be more appropriate for the design of beams with a/d ratio less than 2.0. Due to its rationality, the strut-and-tie model for the design of structures with complex failure mechanism need to be recommended in the IS code of practice.

Studies on fresh properties of limestone calcined clay cement concrete Sendhil Vigneshwar Dhanapal, Prakash Nanthagopalan

Limestone calcined clay cement (LC³) is one of the sustainable cementitious materials with a promising future. In the present investigation, attempts were made to assess the fresh state properties of LC³ concrete and compared with fly ash based concretes of similar strength ranges (30 to 50 MP_a). Fresh concrete properties such as density, slump, slump retention, rheology and setting time were evaluated. From the results, it is evident that LC³ concrete demands relatively higher SP dosage and paste volume than fly ash based concretes for a given slump requirement. Despite higher SP demand, the slump retention and early age strength of LC³ concretes are better than fly ash based concretes. Rheological behavior of LC³ concretes especially with relatively higher viscosity yield better potential against segregation during pumping. It is possible to engineer the rheology of LC³ based concretes to have comparable rheological values for specified applications.

Drying shrinkage of concrete with blended cementitious binders: experimental study and application of models T. Sakthivel, Ravindra Gettu, Radhakrishna G. Pillai

Use of supplementary cementitious materials (SCM_s) has substantially increased in the construction industry in recent years. Long-term data on the effect of different SCM_s on shrinkage and creep are scarce. Also, the appropriate prediction of shrinkage is important to ensure that the design can address the structural requirements when blended concrete systems are used. Towards this, an elaborate experimental programme and application of shrinkage prediction models have been performed on typical blended concretes used in India. The study involved concrete mixes with water to binder ratios (w/b) varying from 0.50 to 0.65, and binary and ternary blended binder contents varying from 280 kg/m³ to 340 kg/m³, having slag and fly ash as partial replacement of cement. The results show that the addition of fly ash and slag does not influence the drying shrinkage strain evolution significantly in comparison with the conventional concrete with same w/b and binder content. Also, it is seen that there could be considerable differences between the shrinkage strains determined experimentally and those predicted by models considered in this study.

Adjustment of RILEM B4 model parameters for better prediction of the shrinkage response of blended cement concrete T. Sakthivel, Ravindra Gettu, Radhakrishna G. Pillai

This paper aims to adjust the model parameters of the B4 and B4^s models using newly collected laboratory data for blended cement concrete systems of strength grades 25 MP^a and 65 MP^a. Based on the data, regression analysis for the B4^s model has been performed to capture the shrinkage response at later ages better. Also, suitable adjustment of the model parameters for aggregate type and the composition of the binder was carried out. After the adjustment, the model seems to be yield improved predictions for the data set.

Measuring workability of concrete- slump test vs rheometers N. Subramanian

Empirical tests like the slump test are often used at site for the measurement of workability of concrete. Most test methods for workability can be classified as single-point and two-point tests. Single-point tests like slump test measure empirically only the yield stress, which alone is not sufficient to evaluate the flow characteristics of concrete. Two-point tests measure both yield stress and plastic viscosity. Although a two-point modified slump test exists, it results in poor correlation of results. Rotational rheometers measure the torque and rotation speed of a bob that circulates inside concrete, based on which yield stress and plastic viscosity are calculated. Several geometries can be used for the bob. Several commercial rheometers also exist. Two types of measurements, viz., flow curve test and stress growth test are possible. All aspects of mixture proportioning of HPC play an important role in its rheology.