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Showing 4 results for Pulse Velocity

Jose Bogas, Augusto Gomes,
Volume 12, Issue 2 (6-2014)

This paper aims to characterize the elastic modulus of structural modified normal density (MND) and lightweight aggregate concrete (LWAC) produced with different types of expanded clay lightweight aggregates (LWA). A comprehensive experimental study was carried out involving different concrete strengths ranging from 30 to 70 MPa and density classes D1.6 to D2.0. The influence of several factors on the LWAC elastic modulus, such as the cement content, initial wetting conditions, type and volume of coarse LWA and the partial replacement of normal weight coarse and fine aggregates by LWA are analyzed. The strength and deformability of LWAC seems to be little affected by the addition of high reactive nanosilica. Reasonable correlations are found between the elastic modulus and the compressive strength or concrete density. The obtained LWAC elastic moduli are compared with those reported in the literature and those estimated from the main normative documents. In general, codes underestimate the LWAC modulus of elasticity by less than 20%. However, the MND modulus of elasticity can be greatly underestimated. In addition, the prediction of LWAC elastic modulus by means of non-destructive ultrasonic tests is studied. Dynamic elasticity modulus and ultrasonic pulse velocity results are reported and high correlated relationships, over 0.95, with the static modulus are established.
R. Perumal, K. Nagamani,
Volume 12, Issue 4 (12-2014)

An experimental study on the impact performance of silica fume concrete and steel fiber reinforced concrete at 28 days and 56 days under the action of repeated dynamic loading was carried out. In this experimental investigation, w/cm ratios of 0.4 and 0.3, silica fume replacement at 10% and 15% and crimped steel fibers with an aspect ratio of 80 were used. Results indicated that addition of fibers in high-performance concrete (HPC) can effectively restrain the initiation and propagation of cracks under stress, and enhance the impact strengths, toughness and ductility of HPC. Pulse velocity test was carried out for quality measurements of high-performance steel fiber reinforced concrete. Steel fibers were observed to have significant effect on flexural strength of concrete. The maximum first crack strength and ultimate failure strength at 28 days were 1.51 times and 1.78 times, respectively at 1.5% volume fraction to that of HPC. Based on the experimental data, failure resistance prediction model was developed with correlation coefficient (R) = 0.96 and absolute variation determined is 1.82%.
Mustafa Sarıdemir, Metin Hakan Severcan, Murat Çiflikli, Serhat Çelikten,
Volume 15, Issue 2 (3-2017)

In this study, the effects of high temperatures on the mechanical and microstructural properties of high strength concretes (HSCs) made with metakaolin (MK) are investigated. For this purpose, the concrete mixtures made with MK were produced with water-binder ratio of 0.2. The mechanical properties of these concretes at 25, 250, 500 and 750 oC temperatures were determined. Besides, the effect of high temperature on the microstructural changes of cementitious matrix, interfaces between aggregate particles-cementitious materials and aggregates of these concretes were inspected by X-ray diffraction, scanning electron microscope and plane polarized transmitted light (PPTL) analyses. The results indicate that the ultrasound pulse velocity, compressive strength, flexural strength and splitting tensile strength values of these concretes decrease especially depending on the increase of the high temperature after 250 oC. The heated concrete specimens were also examined at both macro and micro scales to determine the discoloration, alteration and cracks of HSC at different temperatures. PPTL analyses show that increasing temperature cause impairing of interfaces between aggregate particles and cementitious materials. The results also show that the partial replacement of MK with cement has the best performance on the mechanical properties of HSC.

Özgür Çakır, Muzaffer M. Tüfekçi,
Volume 15, Issue 4 (6-2017)

An experimental program was carried out in order to investigate the usability of recycled coarse aggregate (RCA) concrete with and without ground granulated blast furnace slag (GGBFS). The RCA was derived from concrete having compressive strength of 47.6 MPa. Twelve concrete mixtures having various RCA (0-25-50-100%) and GGBFS (0-30-60%) replacement levels were designed with a water-to-binder (w/b) ratio of 0.50. Fresh concrete properties were observed through workability and slump loss. Compressive strength, tensile splitting strength, bond strength, ultrasonic pulse velocity, water absorption and density of hardened concretes were also determined at 7 and 28 days and the relations between physical properties and mechanical properties of RCA concretes with/without GGBFS were investigated. The RCA content significantly improved the tensile splitting strength of the concrete according to the compressive strength and the use of 60% GGBFS content in RCA concrete had a marginal increasing effect on the tensile splitting strength. The mixes containing 100% RCA was found to be noticeably beneficial in terms of the bond strength and the highest bond strengths were obtained with the use of 60% GGBFS content in RAC for all series at 28 days. However the lowest density and the greatest water absorption was obtained for RAC and an inverse relationship between the density and the water absorption ratio was determined.

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