Interfacial Bond Properties between Normal Strength Concrete and Epoxy Resin Concrete

It is necessary to pay attention to the bonding strength of the interface between precast normal strength concrete (NSC) and cast-in-place epoxy resin concrete (EMR) when using EMR as a repair or filling material or an overlay in bridges’ rehabilitation. However, the performances of epoxy concrete are different due to differential mix ratios; thus, the bonding properties between various epoxy resin concrete and cement concrete are not completely the same. This article investigated the interfacial bond properties between NSC and ERC by direct tensile, push-out, and slant shear test with specimens of special size and structure and observed the interfacial bond strength and corresponding failure modes. The minimum bond strength under direct tension was 0.72 MPa, while the minimum bond strength was 1.71 MPa and 3.19 MPa for the push-out test and slant shear test, respectively. Results indicated that the slant shear test specimens with an inclination angle of 45° are not suitable for the slant shear test due to higher compressive stress. Furthermore, the cohesion and friction coefficient of interface bond strength were calculated inversely in accordance with the results obtained from the corresponding direct tensile and slant shear tests. The minimum cohesion value was 1.71 MPa, and the minimum friction coefficient value was 0.46.

Experimental Investigation of Concrete Transverse Deformations at Relatively High Loading Rates for Interpretation of High Strength Concrete Behavior

Loading rates affect the behavior of concrete specimens from the beginning of the loading process until failure. At rather high loading rates, longitudinal deformations in concrete specimens under a compressive load are practically elastic up until the ultimate limit state. It has been previously demonstrated that transverse deformations effectively indicate high-strength concrete behavior in the entire static loading process range. A theoretical model for cylindrical concrete specimen failure under compressive load, based on a structural phenomenon, has also been proposed. The aim of the present research is experimental verification of using transverse deformations in addition to longitudinal ones for investigating high-strength concrete behavior at the non-elastic stage. This research is based on testing normal-strength concrete cylindrical specimens under compression at relatively high loading rates. The theoretical model of the cracking and failure scheme of the cylindrical specimens are experimentally confirmed. The obtained results demonstrate that it is possible to use transverse deformations for the interpretation of initiation and development of inelastic deformations in high-strength concrete up to class C90 based on the data for normal-strength concrete specimens of class C30 subjected to relatively high loading rates.

Is it reasonable to use high-strength concrete columns under fire conditions?

PurposeThis paper aims to answer two questions. First, are there any differences in the fire performance of columns made of normal and of high-strength concrete? Second, under which circumstances does the fire design govern the cross-sectional dimensions of concrete columns? Is it feasible to replace columns out of normal strength concrete by more slender high-strength concrete columns?Design/methodology/approachThe author conducted numerical studies using the finite element code “Infocad” of the German company “Infograph”. The studies included the effect of different parameters on the fire performance of columns out of normal and high-strength concrete, i.e. the load ratio and eccentricity, boundary conditions and times of fire exposure.FindingsResults from the numerical investigations showed that high-strength concrete columns suffer much more from heating than normal strength concrete columns. This is the outcome of the unfavourable mechanical properties of high-strength concrete at elevated temperatures. Although the relative fire performance of columns out of high-strength concrete is worse than that of columns out of normal strength concrete, initial load reserves are beneficial to achieve even high fire ratings.Originality/valueMany researchers addressed in experimental and numerical studies the fire performance of columns out of normal and high-strength concrete. A special emphasis was often laid on the spalling of fire-exposed high-strength concrete. However, there are no systematic investigations when the fire design governs the cross-sectional dimensions of high-strength concrete columns. Based on a previous comparison of the relative fire performance of columns out of normal and high-strength concrete, this paper, hence, addresses the question whether there is a reasonable lower limit for the use of these columns. This is an important aspect for designers since there is a tendency to replace columns out of normal strength concrete by columns out of high-strength concrete. Higher concrete strengths allow for smaller cross sections of the columns, and designers may, hence, increase the usable space of buildings.

Possibility of using recycled waste medical-glass as fine aggregate in normal-strength concrete

The possibility of using recycled waste medical-glass aggregate (RGA) as a fine aggregate in the production of normal-strength concrete was investigated in this study. The influence of RGA as crushed sand (CS) replacement at different levels (by volume) of 0 – 100% (an interval of 20%) on the engineering properties and durability of concrete was also studied. Results show that the replacement of CS by RGA insignificantly affected the workability and unit weight of fresh concrete mixtures. Besides, using RGA to replace 20 – 60% CS was beneficial in terms of compressive strength, drying shrinkage, and ultrasonic pulse velocity (UPV). At these replacement levels, the dry density values were found to increase and the water absorption values were reduced as well. However, replacing CS with RGA up to 80% and 100% caused a reduction in compressive strength, dry density, and UPV and an increase in water absorption and drying shrinkage of concretes. Closed correlations among the above-mentioned concrete properties were also found in this study. All of the concrete samples obtained compressive strength values higher than the target strength (≥ 25 MPa) and they were classified as very good quality concretes with UPV values of above 4100 m/s. The experimental results demonstrate a high possibility of producing normal-strength concrete with a fine aggregate of RGA as either partially or fully replacement of CS. This also provides an environmentally-friendly solution for recycling waste medical glass in construction materials for sustainable development.