Experimental analysis of basic mechanical properties of concrete upon replacement with silica fume and steel slag

The prime aim in this paper is to find out the effect of Silica Fume and Steel Slag replacements for cement and fine aggregate respectively in the concrete matrix. The research included replacement of constant percentage of silica fume i.e. 10% with cement and varying percentages of steel slag replacements viz. 40%, 45%, 50% and 55% with fine aggregates. It was found from the experimental investigations that optimum results for strength in compression, flexure and split case for concrete were established on 10% of silica fume replacement for steel slag and 50% replacement of steel slag with sand.

Influence of thermoactivation on properties of mineral additives in dry mixtures

Information on the effect of thermal activation of silicate and aluminosilicate rocks used as a filler in dry building mixtures on their reactivity of interaction with lime binder is presented. The change in the distribution of acidic Bronsted and Lewis centers on the filler surface as a result of thermal activation is shown. It was found that the number of Bronsted and Lewis acid centers on the surface of fired clays exceeds the number of the same centers on the surface of unbaked clays. The number of adsorption centers at pKa from 0 to 7 and pKa> 13 on the surface of fired diatomite is 2.435 * 10-5 mol/g, and on the surface of unbaked diatomite -1.678 * 10−5 mol/g. The heat treatment of diatomite at low temperatures (2000C and 3000C) does not significantly affect the values of the compressive strength of the mortar. An increase in the firing temperature to 7000C leads to an increase in strength characteristics up to R = 4.38 MPa. However, the greatest effect is achieved when diatomite is fired at a temperature of t = 9000C. The value of the ultimate strength in compression was R = 5.1 MPa.

Effect of Agents of Initiation of Carbonate Biomineralization on Cement Properties

The paper presents the results of the assessment of the effect of bacterial microorganism Sporosarcinapasteurii and CaCl2 and CH4N2O precursors as agents initiating carbonate mineralization processes on the construction and technical properties of binders. In order to achieve this, a preliminary bacterial solution with precursors was prepared, which was introduced into the system instead of mixing water in the range of 0–10% with interval of 2%. The effect of the bacterial solution as a complex additive on the physical and mechanical properties of cement paste and stone is shown: normal density, setting time, water segragation, strength in compression and bending. The introduction of the solution provides a reduction in the setting time of cement without loss of strength both at the initial and at the final stages of hardening.

EFFECT OF ARTIFICIAL WEATHERING ON PHYSICAL AND MECHANICAL PROPERTIES OF WOOD

ABSTRACT When wood is exposed outdoors, a combination of chemical and mechanical factors and solar radiation contribute to what is described as weathering, being the main degradation agent in this environment. This paper aims to investigate the effect of artificial weathering on mechanical and physical properties of Eucalyptus sp. and Cupiúba (Goupia glabra) woods simulating natural weathering effects. Samples were aged in UV radiation chamber with humidity and temperature control for 100, 200, 300 and 400 hours, considering aging cycles according to ASTM G154 (2006). Wood properties investigated were Conventional value of strength in static bending (fM), Modulus of elasticity in static bending (EM), strength in compression parallel to grain (fc0) and Janka Hardness (fH) according to ABNT NBT 7190 (1997). Effects of artificial weathering on wood properties were evaluated by statistical analysis at 5% significance level. Most of the wood properties investigated did not present significant changes with the aging performed, however, it was noted a decrease in the absolute values of the wood properties absolute values during the aging process. Only fH of Cupiúba wood aged for 100 and 200 hours presented significative performance loss at the significance level considered, which can be related to changes on the wood surface due to weathering exposure.

Effect of Dosage of Redispersible Powders on the Properties of Fine Concrete

The RPP introduction has been established up to 3% by weight of the dry concrete mix is ​​accompanied by a decrease in the fine-grained concrete tensile strength in compression to 40% and in tension during bending to 15%. The relationship between the tensile strength limit in bending and compression for the studied materials is invariant to the cement and RPP type. With the concrete tensile strength in tensile bending increase, there is a weak tendency to a decrease in the adhesion ratio value to the concrete base and tensile strength. The adhesion amount to the concrete base with RPP increasing dosage can either increase or decrease after a certain limit, depending on the cement properties. The maximum increase in adhesion to the concrete base was 37%, while the decrease in the concrete elasticity initial modulus was 26%.

Residual Compressive Strength of High-Strength Concrete Exposed to Elevated Temperatures

High-strength concrete (HSC) has several well-known technical, aesthetic, and economic advantages over normal-strength concrete (NSC), which explains the increasing popularity of the former material in the construction domain. As in the case of NSC, however, high temperature adversely affects HSC mechanical properties even more than in NSC, as indicated by the many studies performed so far on HSC at high temperature (hot properties) or past a thermal cycle at high temperature (residual properties). Since many code provisions concerning concrete properties versus high temperature were developed for ordinary concrete and the available models (in terms of stress-strain relationship) come mostly from the tests on NSC—as the tests on HSC are less numerous—developing predictive relationships for HSC exposed to high temperature is still an open issue, especially with reference to many parameters affecting concrete compressive strength, like temperature as such, heating rate, water-to-binder ratio, and strength in compression, to cite the most relevant parameters. To this purpose, a large database (more than 600 tests) is examined in this paper, which is focused on HSC residual properties and on the variables affecting its residual strength. Available design models from various guidelines, standards, codes, and technical reports are tested against the database, and new regression-based models and design formulae are proposed for HSC strength in compression, after the exposure to high temperature.

EN 206 Conformity Testing for Concrete Strength in Compression

The design of concrete structures in accordance with EN 1992-1-1 adopts the characteristic cylinder compressive strength inits equations. EN 206 provides for conformity testing for concrete strength in compression using 150mm diameter by 300mm length cylinders or 150mm cubes only. The complementary standard to EN 206 in UK, BS 8500 (SS 544 in Singapore, MS 523 in Malaysia) has added provisions (clause 12.2) for the use of 100mm cubes for conformity testing. The conformity criteria for 100mm cube specimens are to be the same as those for 150mm cubes. A series of tests based on 3 selected levels of compressive strength has been conducted to examine the relationship between these 3 types of test specimens for compressive strength of concrete. For each strength level, 100 batches of concrete were produced over a period of several months. The test results are presented with analysis based on the mean of 3 numbers for each type of test specimens prepared from the same batch at each time of preparation. The results of this study for the 3 strength levels support the relationship between standard cylinder compressive strength and standard cube compressive strength in EN 206. In addition, results also support the recommendation that standard 100mm cube compressive strength is equivalent to that of standard 150mm cube compressive strength in BS 8500. The use of the small size cubes and certiication of designed concrete promote sustainability in concrete construction.