Indian Concrete Journal

Experimental investigations on the properties of concrete containing pre-soaked recycled fine aggregate Suman Saha, Rajasekaran C., Manjunath S. Ganiger, Shivakumar Sajjan

Recycled fine aggregate (RFA) becomes very significant and promising alternative materials for natural fine aggregate (river sand) to be used in the production of concrete. But, most of the past research works indicated higher water absorption capacity of RFA as one of the key factor to affect the properties of fresh concrete. Therefore, an experimental attempt has been made to address the issues related to water absorption capacity of RFA by soaking it in water for 24 hours prior to use as alternative fine aggregate for the production of the fresh concrete. Mechanical properties of concrete such as compressive strength, splitting tensile strength, and flexural strength, and durability properties such as resistance against acidic and alkaline environment, chloride permeability test for ordinary Portland cement (OPC) and Portland pozzolana cement (PPC) based concrete mixes made with soaked recycled fine aggregates (SRFA) are determined, and analysed. For OPC, and PPC based concrete, respectively 4.32, and 20.75 % in compressive strength at 28 days; 2.69, and 27.24 % increase in flexural strength; 6.38, and 40 % increase in splitting tensile strength at 28 days were observed for the concrete mixes with SRFA compared to the mixes with RFA. Experimental results indicated notable improvement of the mechanical, and durability properties of concrete mixes when recycled fine aggregates were soaked in water prior to use.

Cement-superplasticizer compatibility and flow properties of binder paste and mortar using marsh cone and flow table method Sheikh Mayesser Mushtaq, Tarun Rajput, Dhiman Basu

Flow behavior of the binder paste renders a fair idea about the properties of high-performance concrete, especially, in the fresh state. Optimisation of the cement matrix phase or the paste phase in terms of fluidity is an important step in the development of high-performance concrete. It is, therefore, imperative to have a simple, effective, and reliable methodology to assess the flow behavior of the paste. Marsh cone test is often employed for this purpose, and limited review of the prior art indicates no standardization of the quantity of the paste corresponding to which the flow time should be measured and the saturation dosage of superplasticizer to be assessed. Rate of flow through the cone orifice may not remain same, and rather decreases with time. This paper investigates the flow time for different quantities of the paste with an aim to assess the optimum quantity to be used with Marsh cone test for the determination of saturation dosage of superplasticizer. The effect of mixing time upon the flow behavior of the paste is next evaluated with the help of Marsh cone test. Further, the mix design of high-performance concrete of compressive strength in the order of 100 MPa often excludes the coarse aggregates, and hence, resulting in a significant increase in the cost of concrete production. This paper also investigates the flow behavior of the mortar prepared with a low sand-to-cement ratio of 0.62, which is typically the case with ~100 MPa concrete utilizing coarse aggregates. Marsh cone test may not be feasible in such a case on account of low water-cement ratio. Conventional flow-table test is indigenously extended for this purpose to make inference on the fluidity of paste and the saturation of superplasticizer dosage. Finally, results of the paper, in principle, enable assessment of the cement-superplasticizer compatibility. Three different brands of cements are used throughout the test program with a well-known brand of superplasticizer.

Flexural capacity of reactive powder concrete Santosh M. Muranal, R. B. Khadiranaikar

Reactive powder concrete (RPC) is classified under ultra high performance concrete (UHPC) vowing to its dense and uniform microstructure and mechanical properties. The design of structures with RPC is governed by its strength and toughness characters. In the present study, RPC with compressive strength of 180 MPa and flexural strength of 25 MPa was produced using local available materials. The flexural strengths of non-fibered and fiber reinforced reactive powder concrete (FRPC) are evaluated. Toughness indices for FRPC are evaluated by loaddeflection test carried on FRPC beam specimens. An analytical expression is proposed to evaluate the flexural strengths of RPC and FRPCs. FRPC beam specimens recorded higher toughness indices when compared with other class of concretes.

Prediction of failure for a slender reinforced concrete column using reliability analysis D. R. Goutham, A. J. Krishnaiah

Reliability analysis for rectangular reinforced concrete columns has been evaluated with varying live loads. The deterministic approach using the SP: 16 (1980)^[17] code is carried for a corner column subjected to axial force and biaxial moments. A typical reinforced cement concrete (RCC) frame is modelled in the ETABS software with geometrical, material, and live load variations. The percentage of rebar of a column is taken from the software tool. The work is conducted for two different orientations of columns in plan and it is presumed that if the rebar percentage obtained after considering the randomness in design parameters exceeds the rebar percentage calculated from the deterministic approach, then the column is said to be in failure. A Monte Carlo simulation technique was employed in the evaluation procedure to predict the probability of failure of the column. A random number generator in excel is employed in order to generate random variables. The randomness in variables relating to geometrical dimensions, material properties, and loading are considered. The study investigates the reliability of the column when design variables are random in nature, and it also extends the plotting of the histogram, probability distribution function, and probability plot.

Assessment of buildings with SSI and without SSI Keerthana Etoori, Pradeep Kumar Ramancharla

This study considers low (5-storey), medium (10-storey), and high-rise (20-storey) buildings on hard, medium, and soft soils according to IS code. These 9 buildings are designed for base shear obtained from IS: 1893-1 (2016)^[11], fixed base and flexible base, respectively. This study shows that buildings designed according IS code are over designed when compared with flexible base. To check safety of these overdesigned buildings, linear dynamic analysis, and pushover analysis were performed. These analyses show that flexible base design is safer, and economical than IS code and fixed base design buildings.