Indian Concrete Journal

Experimental evaluation of stress-strain and modulus of elasticity for structural lightweight concrete using compressometer, linear variable displacement transducer and extensometer Brijesh Singh, Shamsher Bahadur Singh, S K Barai, P. N. Ojha, Rohit Kumar, Puneet Kaura

The huge requirement of aggregates for production of concrete and scarcity of natural aggregates in India calls for an urgent need to explore alternative source of sustainable aggregates. One of the possible source of alternate aggregate can be sintered flyash lightweight aggregate mainly produced using flyash generated as waste from thermal power plants through sintering process. In the present investigation, stressstrain behavior and modulus of elasticity (MOE) for structural lightweight concrete which is a basic property for conducting the linear and non-linear analysis of structural members has been investigated. The accurate determination of stress-strain and MOE of structural lightweight concrete is essential in order to determine maximum allowable deflections, stiffness, story drift for tall buildings, etc. To evaluate MOE, the cylindrical specimens of 150 mm diameter and 300 mm height have been subjected to uniaxial compression under strain controlled mode. The paper highlights the impact of measurement techniques in determining MOE of lightweight concrete made using sintered flyash lightweight coarse aggregate for wide range of w/b from 0.3 to 0.7. The three measurement techniques i.e. (a) Compressometer and Extensometer (b) Linear Variable Displacement Transducer (LVDT) have been adopted for MOE determination. The paper discusses gauge length impact (ratio of length measured along height to specimen height) on the stress vs strain plot of structural lightweight concrete wherein comparison of stress vs strain plots attained from LVDT (gauge length =300 mm) and compressometer/extensometer (gauge length =150/200 mm) has been analyzed. Both measurement techniques for determining MOE have been compared in line with procedure of IS: 516 (Part8/Sec1) (2021)^[13] and ASTM C-469 (2014)^[14] procedures. The stress strain behavior on which MOE of concrete depends has also been compared for both structural lightweight concrete and normal concrete. The difference between ratio of ultimate strain to strain at peak stress for lightweight concrete and normal weight concrete with increase in strength decreases significantly indicating the lightweight concrete is more brittle as compared to normal weight concrete. The stress strain curve of unconfined lightweight concrete indicates linear behavior upto 70-80 % of peak load as compared to normal weight concrete which gives linear behavior upto 35-50 % of peak load

Property assessment during the early age hydration of alkali activated binders using embedded PZT sensors Murali Duddi, Amarteja Kocherla, Kolluru V L Subramaniam

The lead, zirconate, and titanium (PZT) sensor is developed to monitor the changes in alkali activated fly ash-slag binders (AAFS). The durability of PZT sensors is verified for their suitability to monitor changes in high alkaline cementitious mediums. The PZT sensor is used to monitor the changes in workability, set behavior and elastic property development in AAFS binders. The sensors are placed in mixes with different fly ash and slag compositions to understand the influence of fly ash and slag ratio on properties of AAFS binders. The electrical impedance (EI) response of the PZT sensor is extracted to monitor the changes in workability and set behavior of the mixes. The changes in the elastic modulus of the AAFS binders with hydration are measured from the vibration response of the cylinder samples extracted using the embedded sensors. The isothermal calorimetry is performed to measure the kinetics of hydrations of these binders. The changes in EI response parameters are correlated with the changes in kinetics of hydration to validate the sensitivity of the EI parameters to monitor the changes in workability and set behavior. The embedded PZT sensors are very effective in capturing the changes in workability, state transition and elastic properties.

The workability, set behavior and elastic property development in AAFS binder system is highly influenced by the slag content in the mix. The hardened state of these AAFS binders achieved in 2 hours of hydration and the changes in elastic modulus are minimal after the 3 days of hydration. The uncontrolled setting, in AAFS binders needs careful study to transform these materials from laboratory to field.

Effect of precursors on the properties of one-part alkali-activated composites S. K. Singh, Yasmeen Qureshi, Biswajit Pal

Portland cement has been the most reliable cementitious binder for over 200 years but is responsible for more than 7 % of global greenhouse gas emissions. The alkali-activated binder (AAB) has been developed to reduce carbon emissions significantly. The application of conventional (two-part) alkali-activated binders is primarily limited to small-scale projects owing to several challenges, including transportation, mixing with liquid alkali solutions and placing. Therefore, this study explores an alternative approach to developing binary and ternary binders of one-part AABs. The precursors fly ash (FA) and Ground granulated blast furnace slag (GGBFS) binary binder utilise a solid activator (sodium metasilicate pentahydrate) and agroindustrial waste materials. In contrast, rice husk ash (RHA) was added as a precursor for the ternary binder. Various mixtures were fabricated with different proportions of source materials (FA, GGBFS, and RHA) and curing temperatures (ambient and at 80° C for 3 hours). Based on the optimum strength of binary pastes, alkali-activated concrete (AAC) was developed. The AAC was then employed for different mechanical (split tensile and compressive strength) and durability tests (resistance to sulphate attack and water absorption) to assess its properties. Experimental studies revealed that an AAB composed of a 30:70 weight ratio of FA to GGBFS and a 12 % solid alkali activator achieved a maximum compressive strength of 25.32 MPa under ambient curing conditions. In addition, the results of the ternary paste indicate that up to 10 % of the addition of RHA into the mix resulted in improved compressive strength. SEM analysis also demonstrated the formation of a denser micro-structure under heat curing and at 10 % RHA-based ternary mix. Further, adding basalt fibres (0.5 % volume fraction of concrete) does not significantly impact the mechanical and durability properties. These findings suggest that alternative sustainable binders effectively utilise industrial waste and could reduce the carbon footprint significantly.

Effect of carbonation on properties of red mud incorporated portland cement Saranyadevi Duraisamy, Piyush Chaunsali

Red mud is a by-product of aluminium manufacturing. Due to high alkalinity and the presence of heavy metals, landfilling of red mud poses an environmental challenge. This paper investigates the effect of pre-curing, moist curing, and CO₂ curing on compressive strength and microstructural characteristics of red mud-incorporated cementitious system. The strength results indicate that the 4-hour accelerated CO₂ curing is comparable to 7-day moist curing. Calcite is the predominant phase present in CO₂-cured samples, contributing to early-age strength. Also, the clinker phases (alite and belite) reacted with CO₂. The study paves the way for red mud utilization via CO₂ mineralization.

Utilization of low-grade limestone for producing alternative low-CO₂ cement Bipina Thaivalappil, Piyush Chaunsali

Calcium sulfoaluminate-belite (CSAB) cement is a lowCO₂ alternative binder to Portland cement (PC) for various applications. Additionally, CSAB binders are rapid hardening, acid resistant, and help with shrinkage compensation. However, the commercial production of CSAB cement is limited due to the increased cost of raw materials and limited understanding of the composition-performance relationship of CSAB-based binders. The CaO content in the CSAB clinker raw mix is lower compared to PC, allowing the possibility of utilizing lowgrade limestone for its production. This paper investigates the feasibility of using low-grade limestone (<40 % CaO) with clayey and silicious impurities as an alternative raw material source to partially replace high-grade limestone. The influence of raw mix composition on the clinker phase assemblage and hydration was investigated using different characterization techniques. The successful synthesis of CSAB cement was demonstrated with up to 20 % (by weight) low-grade limestone incorporation in the raw mix. The clinker phase assemblage, hydration reactions, microstructure development, and mechanical performance in the synthesized CSAB cement was comparable to that of a commercial CSAB cement having similar composition.