Mechanical Properties Of Structural Concrete Research Articles

Mejoramiento de las Propiedades Mecánicas del Concreto Estructural Utilizando Microporoso Etileno Acetato de Vinilo

Over the years, the world has tried to increase the recycling of materials, especially those of artificial origin, this in order to produce compounds that are sustainable and sustainable. Among these materials, concrete stands out as a versatile element, to which different external agents can be added; however, since many of them are not compatible with aggregates, cement or water, can cause some alterations in their mechanical performance. Therefore, the present investigation addressed the study of an artificial material called Microporous Ethylene Vinyl Acetate (MEVA), in order to evaluate its influence on the mechanical properties of structural concrete. MEVA additions were used in ranges of 5.00 %, 10.00 %, 15.00 % and 20.00 % with respect to the volume of concrete, to analyze its behavior in the mix, both in physical and mechanical properties. The results show that the workability and unit weight are affected by the increase in MEVA. Despite this, the mechanical performance showed significant increases in the compressive strength of 8.81 %, tensile of 22.86 %, flexion of 24.51 % and modulus of elasticity of 2.12 %, with the addition of 5.00 % of MEVA after 28 days. Nevertheless, at higher doses there is a reduction in said strengths. For these reasons, it is concluded that the incorporation of MEVA at 5.00 % greatly improves the mechanical properties of concrete for structural use, in relation to the theoretical design strength of 21.00 MPa.

Recent efforts on investigating the effects of recycled rubber content on the mechanical properties of structural concrete

Recent efforts on investigating the effects of recycled rubber content on the mechanical properties of structural concrete

Nopal extract and aloe vera to improve structural concrete exposed to saline environments

The objective of this study was to examine the impact of Nopal (N) and Aloe Vera (AV) on the physical and mechanical properties of structural concrete in saline environments. Concrete with a compressive strength of 245 kg/cm² was used, adding N and AV extracted from natural plants in the study region. A total of 130 cylindrical specimens, 40 prismatic specimens, and 10 fresh mix samples were analyzed. Percentages of Nopal (2%, 6%, and 10%), Aloe Vera (0.5%, 1.5%, and 3%), and mixed (2%N + 0.5%AV, 6%N + 1.5%AV, 10%N + 3%AV) were added based on the weight of the cement. The control group contained no additives. The best results were obtained with the 2%N + 0.5%AV samples, with the highest compressive strength of 443.4 kg/cm² at 28 days and 445.4 kg/cm² at 56 days, a tensile strength of 41.4 kg/cm² at 28 days, a flexural strength of 66.4 kg/cm² at 56 days and 70.9 kg/cm² at 90 days of curing. The corrosion resistance decreased by a maximum of 0.22 mm/year. The physical and mechanical properties were optimized with the proportion of 2%N + 0.5%AV, indicating that the mixing matrix becomes more compact, and the carbonation rate is reduced, resulting in greater strength and durability.

Effect of recycled rubber aggregate size on fracture and other mechanical properties of structural concrete

Rubberised concrete (RC) is a green and environmentally friendly concrete type that can be used as a sustainable production material. However, investigations on the structural applications of RC are limited due to its increased cost and decrease in strength. In this study, economical mixture designs were formulated with low-level replacements of rubber aggregates from recycled end-of-life tyres, as a prospective approach. The size effect with coarse (15 mm tyre shreds) and fine (2–4 mm tyre crumbs) rubber aggregates on the fresh and mechanical properties of structural concrete, specifically its fracture properties, was investigated, incorporating preliminary testing and constitutive models. The damage evaluation and characteristics of Mode I fracture behaviour of RC were investigated using three-point bending tests on notched beams. Using digital image correlation which possibly can be used to replace the conventional tools, the crack patterns on the beams were detected and crack mouth opening displacements were measured. The rubber replacements led to crack bridging effects. Overall, the results indicate that addition of recycled tyre aggregates at low percentages results in improved ductility and higher energy absorption and thereby improving the toughness of concrete, with marginal impacts on its strength and other properties. Furthermore, the selected mathematical models for compression and fracture can be used to evaluate the performance of RC structural elements with different rubber replacement levels. The modified RC can be potentially applied to structural components for earthquake resistance, integral bridges, or impact resistant road barriers.

Analysis of the mechanical properties of the concrete with partial substitution of the kind’s aggregate glass powder

In this study, the influence of partial introduction as glass as fine aggregate on the composition of simple concrete is analyzed, considering that sand (fine aggregate currently used) has been used on a large scale in civil construction over the years and has been affecting the environment. The main objective of this research was to analyze the mechanical properties of concrete, partially replacing the natural sand with another fine aggregate made from glass residues, evaluating the behavior presented at the end of each test using different percentages of this material as fine aggregate in the concrete composition. From an experimental methodology that consisted of determining an object of study (concrete), selecting the variable that would possibly be able to influence it (glass powder) and defining the ways of controlling and observing the effects that the variable would produce on the object, an interpretation of how the mechanical properties of the glass powder that affect the performance of structural concrete is presented. The granulometry was subsequently analyzed, the tests carried out both in the fresh and hardened state of the concrete, and identified that the glass in a certain percentage proves to be viable. Finally, it can be concluded that the partial inclusion of glass affects the mechanical properties of structural concrete, and can present quite satisfactory results, both related to the environment, since the sand would not be used entirely as fine aggregate or in reaching a resistance suitable for its final use.

Fire resistance of corroded high-strength structural concrete

Purpose The exposure of reinforced concrete structures such as high-rise residential buildings, bridges and piers to saline environments, including exposure to de-icing salts, increases their susceptibility to corrosion of the reinforcing steel. The exposure to fire can further deteriorate the structural integrity of corroded concrete structures. This combined effect of corrosion damage and fire exposure is not generally addressed in the structural concrete design codes. The synergistic combination of the effects of corrosion and fire forms the basis of this paper. Design/methodology/approach Concrete beam specimens with different strengths were prepared, moist-cured and corroded with impressed current. Later, they were “crack-scored” for corrosion evaluation, after which half were exposed to fire in a gas kiln. The fire damage was evaluated by nondestructive testing using ultrasonic pulse velocity. Next, all specimens were tested for residual flexural strength. They were then autopsied, and the level of corrosion was determined based on mass loss of the reinforcement. Findings For corroded specimens, the flexural capacity loss because of fire exposure increases as the compressive strength increases. In general, the higher the crack score, the higher the corresponding mass loss, unless some partial/segmental debonding of the reinforcement occurred. The degree of corrosion increases with decreasing compressive strength. The residual moment capacity, based on analytically determined capacities of uncorroded and nonfire-exposed beams, was significantly lower than those of uncorroded beams exposed to fire. Originality/value The combined effects of corrosion and fire on the mechanical properties of structural concrete are relatively unknown, and no guidance is available in the existing design codes to address this issue. Accordingly, the findings of the paper are expected to be valuable to both researchers and design engineers and can be regarded as the initial investigation on this topic.

Influence of recycled coarse aggregates characteristics on mechanical properties of structural concrete

This work studies with the influence of recycled coarse aggregates features on the mechanical properties of structural concrete. Recycled concrete is characterised by replacing different percentages of natural coarse aggregate with recycled coarse aggregate (0, 20, 50 and 100%) and two different water-to-cement ratios .50 and .65. The experimental program was carried out at the two laboratories: one at the University of A Coruña and another at the Università Politecnica delle Marche (Italy). For said purpose, two different recycled aggregates were used, with different water absorptions and compositions. Results obtained allowed the authors to establish different mechanical behaviour of recycled concrete (compressive strength, tensile splitting strength and modulus of elasticity) due to different replacement percentages and characteristics of the recycled aggregates.

Characteristics of structural concrete containing fluorosilicate-based admixture (FBA) for improving water-tightness

Water-tightness performance of concrete is very important from the aspects of water-proof and durability of the reinforced concrete structure. In this study, fluorosilicate-based admixture (FBA) was used for concrete to improve the water-tightness. This paper provides the results of experimental program on the mechanical properties of structural concrete containing different levels of FBA. The experimental program was planned to investigate the effects of FBA for improving the water-tightness on the fresh and hardened properties of structural concrete. Experimental program focused on concrete mixtures with fixed water-to-binder (W/B) ratio of 0.50 and a constant total binder content of 360kg/m3. The added percentages of FBA by mass of cement were: 0%, 0.5%, 1.0%, 1.5% and 2.0%. The test results show that as the added percentage of FBA increased, the workability of fresh concrete as well as the mechanical properties including the water-tightness of hardened concrete improved. Also the addition of FBA effectively reduced free shrinkage strain of structural concrete, and resulted in a considerable reduction in shrinkage cracks.

Influence of the volume fraction and the nature of fine lightweight aggregates on the thermal and mechanical properties of structural concrete

The results of investigations on thermal and mechanical properties of lightweight aggregate concretes according to mixture parameter are reported. Seven types of fine and coarse lightweight aggregates from three different natures were used. The aggregates in mixes were a combination of coarse lightweight aggregate with fine normal-weight aggregate and/or fine lightweight aggregate. The replacement of fine normal weight aggregate by fine lightweight aggregate reduces concrete strength but improves its thermal performance. Detailed analysis of the influence of the nature and quality of aggregates on the concrete properties is provided. The experiment data allows to investigate the relation between mechanical properties and thermal conductivity for studied concretes in order to optimize the strength/insulation ratio. A wide range of “insulated” lightweight aggregate concretes is performed whose strength class ranges from LC20/22 to LC40/44 and thermal conductivity ranges from 0.43 to 0.73W/mK.

Development of an ultrasonic experimental device to characterise concrete for structural repair

Various non-destructive testing methods, based on the propagation of ultrasonic waves, can be used to characterise the mechanical properties of structural concrete in situ. The results obtained however are heavily influenced by both water content and concrete mix design. To overcome these biases, it is necessary to recalibrate the results on a small number of cores, whose water content has been laboratory-controlled. To this end, an experimental device designed around the transmission of bulk waves has been developed. The aim of this paper is to introduce and describe such a device, which is able to take into account specimen size, centre frequency and ease of use. The studied mixes herein are composed of wet shotcrete, dry shotcrete and concrete that has been formed and manually set. Measurement results show the evolution in wave velocities relative to four degrees of saturation. Moreover, measurement uncertainties in the values of velocities, Young’s modulus, shear modulus and Poisson’s ratio are quantified.

Apparatus for Testing Concrete under Multiaxial Compression at Elevated Temperature (mac2T)

This paper describes a new test facility for determining material mechanical properties of structural concrete. The novel facility subjects 100 mm cubic concrete specimens to true multiaxial compression (σ1 ≠ σ2 ≠ σ3) up to 400 MPa at temperatures of up to 300°C. Forces are delivered through three independent loading frames equipped with servo-controlled hydraulic actuators creating uniform displacement boundary conditions via rigid platens. Specimen deformation is calculated from displacements measured to an accuracy of 10−6 m using a system of six laser interferometers. The combination of stiff loading frames, rigid platens, an accurate and reliable strain measurement system and a fast control system enables investigation of the material response in the post-peak range. The in-house developed control software allows complex multi-stage experiments involving (i) load and temperature cycling, (ii) small stress probes and (iii) arbitrary (pre-defined) loading paths. The program also enables experiments in which the values of the control parameters and the execution of the test sequences depend on the response of the specimen during the test. The capabilities of the facility are illustrated in this paper by experiments determining the effects of different heat-load regimes on the strength and stiffness of the material and tests identifying the tangent stiffness matrix of the material and the associated changes in the acoustic tensor under multiaxial compression.