14.00 The purpose of the current research was to evaluate the influence of nano and micro silica on compressive strength properties of cement concrete. Silica nanoparticles of size around 350 nm are synthesized by Stober’s method using Tetra Ethyl Silicate (TEOS), Ethanol and ammonia solution. The synthesized silica particles are characterized using Dynamic Light Scattering (DLS), Scanning Electron Microscopy (SEM) and Fourier Transform Infrared Spectroscopy (FTIR). Four different batches of sixteen cubes each of dimension 150 mm x 150 mm x 150 mm were prepared by mixing the cement with nano and micro silica, Ultra pozzolana, fine and coarse aggregates by incorporating 0.8% CF 615. The first batch composed of cement, fine aggregate and coarse aggregate and 0.8% CF 615 was considered as a reference batch. Same mix design of proportion 1:1.4:2.1 was followed for remaining mixes by replacing 1% of cement by nano silica, micro silica and Ultra pozzolana. The compressive strength tests of the above mixes are measured using Universal Testing Machine and the results were compared with the control mix. The results demonstrated that the sample were prepared using Ultra pozzolana with 0.8% CF 615, was found to have better strength of 37.45 N/mm 2 compared to other samples. Normal 0 false false false EN-US X-NONE X-NONE /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin:0in; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:"Calibri","sans-serif";}
800x600 Early prediction of strength is crucial in planning for stripping off the formworks and preventing non-working days in concrete construction projects. There are several empirical correlations which allow estimation of concrete strength from early age results. However these correlations have limitations in application. This study established an experimental database which comprised of 382 datasets of strength tests of ordinary Portland cement concrete. These tests were performed over a period of 8 years as part of QA/QC program on 51 construction projects in the Province of Guilan, Northern Iran. From the data, strength ratios between ages (27 and 8 days), (42 and 7 days), (42 and 14 days), and (42 and 28 days) were analysed. New linear and power relations were proposed for estimating 28- and 42-day strength values. Analyses of relative errors along with cumulative probability approach revealed that three well-known models from literature were inaccurate in prediction of strength. It was found out that a correlation by Slater (1926) over-predicted 28-day strength from 7-day test data. Furthermore, the ACI committee 209 (1997) and CEB-FIP (1990) models under-predicted 42-day strength using 28-day strength results. This research should assist in the global, yet simple, understanding of concrete strength development with age. Normal 0 false false false EN-CA X-NONE AR-SA MicrosoftInternetExplorer4 /* Style Definitions */ table.MsoNormalTable {mso-style-name:Table Normal; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-parent:; mso-padding-alt:0cm 5.4pt 0cm 5.4pt; mso-para-margin:0cm; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:Times New Roman,serif;}
Research towards producing environmental friendly cement sand brick stems out from the environmental problem caused by dumping of cockle shell by cockle trade and the increasing river sand mining. This paper discusses the effect of finely crushed cockle shell as partial fine aggregate replacement towards compressive strength, flexural strength and water absorption of cement sand brick. A total of six mixes have been used in this experimental work. Brick produced 100% river sand is considered as control specimen. Another type of mix was prepared by adding a range of crushed cockle shell that is 10%, 20%, 30%, 40% and 50% as partial fine aggregate replacement. All mixes were subjected to water curing until the testing age. Both compressive strength test and flexural strength were conducted at 7, 28 and 60 days. The findings shows that integration of 30% finely crushed cockle shell increase the compressive strength and flexural strength of brick. The same mix also exhibits the lowest water absorption value. Utilization of crushed cockle shell as partial fine aggregate replacement that acts as filler makes the internal structure of brick become denser and stronger. Success in incorporating cockle shell waste in brick production would assist in reducing quantity of shell disposed by cockle trade as solid waste and lower the consumption of natural river sand.
This study aims to monitor the damage growth of plain and fly ash concrete prisms with different curing periods under cyclic incremental loading using acoustic emission (AE) parameters. Higher flexural strength was observed for 28 days cured plain and fly ash concrete prisms as compared to 7 days cured. AE results for 7 days cured plain and fly ash concrete prisms have shown that, Kaiser effect exist in first two loading cycles and from third cycle onwards significant AE activity occurs prior to the previous cycle's maximum load. This is an indication of the start of damage almost at the same load in both the concretes. For 28 days cured fly ash concrete, AE activity during cyclic loading is observed only at 20 kN load as compared to plain concrete in which it occurs at 12 kN load. This shows that cyclic load flexural resistance of fly ash concrete for damage accumulation is higher than that of plain concrete. Load ratio of both types of concrete has been determined during each cycle. Decrease in trend of load ratio with loading cycle is an indication of damage growth. Higher load ratio in 28 days cured fly ash concrete shows addition of fly ash with extended curing which resists damage accumulation. An attempt has been made to classify damage levels during each cycles using NDIS 2421 standard and compared the types of damage in both plain and fly ash concretes.
