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Recently, barium carbonate nanomaterial has been shown to be a proven versatile candidate for the catalysis and sensor applications. The catalytic and sensing efficiency can be improved by making barium carbonate composite with a suitable transition element. In this regard, the preparation of barium carbonate and its composite with nickel during the synthesis process is presented with the composite-hydroxide-mediated method, an effective, feasible, and low-temperature synthesis route. The nanomaterial produced is monitored for the structural and optical properties with various diagnostic methods. The X-ray diffraction results show the presence of orthorhombic structure of barium carbonate in both pure and 5% nickel samples. A mixed structure is formed with the phases of barium carbonate, Ba(NO 3 ) 2 , and Ni(NO 3 ) 2 for the sample with 15% nickel. The average crystallite size estimated is in the range of 14-22 nm. The scanning electron microscope pictures captured on silicon (Si) covered with the product material reveal interesting rods, needle, and flower-type morphological features. The bandgap energy obtained by diffused reflectance spectroscopy is in the expected range of 5.48-5.71 eV. The proposed method seems effective to provide a feasible route for the synthesis of a broad range of nanomaterials for research purposes.

In this study, the role of a locally available rice husk ash (RHA) in reducing early-age shrinkage of high performance concrete (HPC) after evaluating its pozzolanic reactivity was evaluated. The X-ray diffraction (XRD) and energy dispersive X-ray (EDX) analyses were performed after burning rice husk to 700 and 950 • C. Presence of relatively high deposits of amorphous siliceous phases in RHA at 700 • C indicated its pozzolanic potential. Subsequently, this RHA was ground to desired fineness, followed by sieving through sieve No. 200. Eventually, the fine RHA was used as a substitute of cement in different percentages (10, 15, and 20%) to evaluate its influence in mitigating autogenous shrinkage in concrete. Prismatic concrete beams (100 × 100 × 800 mm) were cast to measure autogenous shrinkage along with cylinders (150 mm dia. x 300 mm height) to test compressive strength of concrete. The results indicated a slight increase in compression strength with addition of 10% RHA, which however, reversed and slightly reduced in concretes containing 15 and 20% RHA. Unlike strength results, the trend of autogenous shrinkage was rather uniform as the rate as well as the amount of early-age autogenous shrinkage continued to decrease with increasing percentage of RHA. Moreover, despite of reduced rate during first 24 h, thereafter, the effect of 20% RHA on further reduction of autogenous shrinkage was insignificant and ended up only slightly lesser than the 15% RHA concrete at 7 days. Finally, the control cement sand mortar and mortar containing 15% RHA were cast to further validate the pozzolanic reactivity of RHA through scanning electron microscopy (SEM), EDX, and thermogravimetric analysis (TGA) tests. An observation of reduced amount of calcium hydroxide (Ca(OH) 2) in RHA mortar samples indicating its excellent pozzolanic potential when used as a partial substitute of cement in HPC.

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