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on fresh concrete properties (workability) as well as the mechanical properties (compressive strength, flexural strength, split tensile strength) of hardened concrete. 2 Materials and test procedures F-GFA is used as fine aggregate throughout this

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Pollack Periodica
Authors: Silvia Patachia, Georgeta Moise, Hulusi Ozkul, Ozgur Ekincioglu, and Catalin Croitoru

. Flexural strength and porosity of cement, Nature , Vol. 289, 1982, p. 388–390. Kendall K. Flexural strength and porosity of cement Nature

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twenty four specimens for each mix to investigate compressive, splitting tensile and flexural strength. The specimens were tested for curing period of 7 and 28 days. The details of test specimens with different curing period are depicted in Table 3

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and the values were averaged. Flexural strength tests were carried out according to ASTM D790–07 on a Universal Testing Machine. Following the standard, the tests were conducted at 23 ± 2 °C, 50 ± 5% RH. The thickness, width, and length of the flexural

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density, compressive strength, tensile strength, and flexural strength were studied to conclude the mechanical properties of the concrete specimens developed with AD-G-GFA and OD-G-GFA, which were then compared with the control concrete specimens developed

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test was carried out to determine the flexure strength of modified concrete. The result of the glycoluril modified concrete is shown in Fig. 3 . In concrete with 3% glycoluril-formaldehyde, maximum flexural strength is revealed among other mechanical

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Abstract  

The chemical corrosion and the mechanical strength were studied in cement mortars containing an additive of FBCC under conditions of long-term action of sodium sulphate solution or saturated brine. The observations have shown that saturated brine is a more aggressive agent, since it leaches Ca(OH)2 and contributes to the decomposition of the C-S-H phase thus worsening the compressive strength as compared with that of mortars kept in water. The addition of 20% FBCC inhibits the leaching process and counteracts the decrease of compressive strength in mortars kept in brine. On the other hand, sodium sulphate solution changes favourably the mortar microstructure, increases of the content of small pores and improves both the compressive and the flexural strengths, as compared with those of a mortar kept in water.

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Calorimetry in the studies of cement hydration

Setting and hardening of Portland cement–calcium aluminate cement mixtures

Journal of Thermal Analysis and Calorimetry
Authors: Marek Gawlicki, Wiesława Nocuń-Wczelik, and Łukasz Bąk

Abstract  

Calorimetry was applied to an investigation of the early hydration of Portland cement (PC)–calcium aluminate cement (CAC) pastes. The heat evolution measurements were related to the strength tests on small cylindrical samples and standard mortar bars. Different heat-evolution profiles were observed, depending on the calcium aluminate cement/Portland cement ratio. The significant modification of Portland cement heat evolution profile within a few hours after mixing with water was observed generally in pastes containing up to 25% CAC. On the other hand the CAC hydration acceleration effect was also obtained with the 10% and 20% addition of Portland cement. As one could expect the compressive and flexural strength development was more or less changed—reduced in the presence of larger amount of the second component in the mixture, presumably because of the internal cracks generated by expansive calcium sulfoaluminate formation.

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Abstract  

Crystallization, morphology and mechanical properties of a spodumene-diopside glass ceramics with adding different amount of CaO and MgO in Li2O-Al2O3-2SiO2 were investigated. With CaO and MgO addition, the crystallization temperature (T p) decreased, the value of Avrami constant (n) decreased from 3.2±0.3 to 1.4±0.2, the activation energy (E) increased from 299±3 kJ mol−1 to 537±5 kJ mol−1. The crystalline phases precipitated were h-quartz solid solution, β-spodumene and diopside. The mechanism of crystallization of the glass ceramics changed from bulk crystallization to surface crystallization. The grain sizes and thermal expansion coefficients increased while flexural strength and fracture toughness of the glass-ceramics increased first, and then decreased. The mechanical properties were correlated with crystallization and morphology of glass ceramics.

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Abstract  

In situ developments of platelike spodumene–diopside grains were obtained by controlled devitrification of the complex system Li2O–CaO–MgO–Al2O3–SiO2 glass. The crystallization mechanisms of spodumene–diopside glass were measured by isothermal and non-isothermal processes using classical and differential thermal analysis techniques. The Avrami constant n was 2.0–2.1, indicating two-dimensional crystal growth and platelike grains. The crystalline phases precipitated first were high-quartzs.s., then transformed to β-spodumene and diopside. The Flexural strength, fracture toughness and thermal shock resistance (in 20°C water) increased from 145 MPa, 1.3 MPa m1/2, 800°C (pure spodumene) to 197 MPa, 2.9 MPa m1/2 and 920°C (spodumene–diopside) with low thermal expansion coefficient (from 3∼9·10–7 to 11.8·10–7 K–1). This mean in situ developments of platelike spodumene–diopside grains reinforced the low thermal expansion coefficient glass-ceramics.

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