Multiphase Model for Predicting the Thermal Conductivity of Cement Paste and Its Applications

Thermal conductivity plays a significant role in controlling thermal cracking of cement-based materials. In this study, the thermal conductivity of cement paste at an early age was measured by the hot plate method. The test results showed that the thermal conductivity of cement paste decreased with the increase of water/cement ratio and curing age. Meanwhile, a multiphase model for the thermal conductivity of cement paste was proposed and used to study the influence of saturation and curing temperature on the thermal conductivity of cement paste. To determine the parameters involved in this model, the thermal conductivity of each phase in cement paste was calculated by the molecular dynamic simulation method, and the hydration of cement was simulated by the Virtual Cement and Concrete Testing Laboratory. The inversion results showed that the relative error between experimental and simulation results lay between 1.1% and 6.5%. The thermal conductivity of paste in the saturated condition was 14.9–32.3% higher than that in the dry state. With the curing temperature increasing from 10 °C to 60 °C, the thermal conductivity of cement paste decreased by 3.9–4.9% depending on the water/cement ratio.

Reduction of cement content using graded aggregates in concrete production

The aim of this project was to reduce cement content in concrete mixtures by changing the aggregate grading. For this purpose, concrete mixtures were made with aggregates having different shapes, textures, and grading. However, the workability of concrete mix depends on its paste volume, paste composition, and the type of aggregate used. Concrete testing was performed, and concrete properties including slump, compressive strength, and tensile splitting test were tested. The effect of aggregate shape on workability was evaluated by comparing one aggregate combination to another. It was found that the aggregate combination with S/A= 0.4 GR-B-CA+NA-A-FA had optimum workability properties and generally, GR-B-CA+NA-A-FA consistently had the highest workability, as well as the highest paste volume demand. This can be attributed to its poor grading as a result of the gaps in GR-B-CA content. Compared with NA-A-CA + NA-A-FA, it resulted in concrete mixtures with lower paste volume demand.

The compressive strength of steel fibre reinforced concrete obtained by testing cubes and cylinders

There are two most popular approaches to determining the compressive strength of concrete: testing cubes, testing cylinders. The use of different samples gives different results, which are intended to characterize one parameter of the material compressive strength. The article discusses a general approach to determining the compressive strength of cylinders and cubes. The analysis of the factors influencing the transition coefficients when testing the cylinder samples with the ratio of height to diameter is less than 2. The results of testing cubes and cylinders for compression made of fiber-reinforced concrete are presented.

Effect of glass and carbon fibres on the compressive and flexural strength of the polymer concrete composite

This article is focused on testing the mechanical properties of polymer concrete testing samples. After a thorough literature search, the basic conditions of the research were determined and under the standards, three types of samples of special new concrete mixtures were created as a building element for special CNC machines. The samples were subjected to the research of the influence of used fillers, binders and additives on their properties. Testing was carried out in a certified laboratory and included checking the dimensions of the test bodies, weighing on the calibrated weight, determining the volumetric weight, determining the maximum load of the testing samples using special devices and then determining the compressive strength, or flexural tensile strength according to the relevant formulas. The final part of the testing also examined the morphology and mapping of the chemical composition with a focus on carbon, oxygen and aluminum using an electron microscope. The obtained results clearly show an increase in tensile and compressive strength using dispersed carbon fibre reinforcement of approximately 4 MPa. The conclusion of the article provides an overall summary of the results obtained and a summary of the features.

Experimental Investigations of Concrete on Slag Portland Cement as a Coating Material for Agricultural Aerodromes

The results of concrete testing on sulphate-resistant slag Portland cement for rigid coating of agricultural roads and aerodromes are presented in the paper. The results of experimental investigations of samples in the form of cubes on compressive strength and samples in the form of prisms on bending strength under different hardening conditions and at different water-cement ratios are presented. Selection of hardening conditions of concrete on sulphate-resistant slag Portland cement was made based on achievement of quality indicators no worse than in concrete on Portland cement. The expediency of introducing into the concrete organic surface-active additives - lignosulfonates in order to achieve the required strength is grounded. It is proved experimentally that the proposed concrete has sufficient frost resistance.

The The Characterization and Modeling the Mechanical Properties of High Strength Concrete (HSC) Modified with Fly Ash (FA)

One of the main challenges facing Civil Engineering community is to modify cement quantity in the mix design by admixtures to enhance the mechanical properties. According to more than 1000 data from literature, mechanical characteristics of concrete modified with FA were discussed. The statistical variation with modeling were achieved by set of data. The cement was replaced up to 70% with FA (weight of dry cement) and by cube of concrete testing up to 90 days of curing time and different w/c ratio. The compressive strength of concrete varied from 18-67 MPa, while, for modified concrete with FA, compressive strength ranged from 21-94 MPa, tensile strength ranged from 1-9 MPa and flexural strengths ranged from 3 - 10 MPa. The w/c ratio of concrete modified with FA varied from 0.24-0.53, also the FA content varied from 0-50 %. Vipulanandan correlation model was effective by connecting mechanical properties and compare with Hoek-Brown model. The nonlinear model was used to investigate the effect of FA on properties of normal and high strength concrete. Study results presented a worthy correlation between compressive strength and curing time, w/c ratio and FA content. By using the interactive linked (model) for compressive, tensile, and flexural strengths of concrete quantified well as a function of w/c ratio, curing time and FA content by using a nonlinear relationship.