Long-term Strength Of Concrete Research Articles

The Effect of Incorporating Industrials Wastewater on Durability and Long-Term Strength of Concrete.

Concrete, as one of the essential construction materials, is responsible for a vast amount of emissions. Using recycled materials and gray water can considerably contribute to the sustainability aspect of concrete production. Thus, finding a proper replacement for fresh water in the production of concrete is significant. The usage of industrial wastewater instead of water in concrete is considered in this paper. In this study, 450 concrete samples are produced with different amounts of wastewater. The mechanical parameters, such as slump, compressive strength, water absorption, tensile strength, electrical resistivity, rapid freezing, half-cell potential and appearance, are investigated, and a specific concentration and impurities of wastewater that cause a 10% compressive strength reduction were found. The results showed that the usage of industrial wastewater does not significantly change the main characteristics of concrete. Although increasing the concentration of wastewater can decrease the durability and strength features of concrete nonlinearly, the negative effects on durability tests are more conspicuous, as utilizing concentrated wastewaters disrupt the formation of appropriate air voids, pore connectivity and pore-size distribution in the concrete.

Fracture Mechanics when Studying the Long-Term Strength of Concrete

The results of experimental and theoretical studies of the process of destruction of concrete by the methods of fracture mechanics are considered. Results of studies of long-term strength, durability and deformability of concrete subjected to a preliminary short-term temperature action up to 300° C and 400° C under load and without load are presented. It is shown that after short-term heating up to 300о С the long-term strength of concrete decreases insignificantly. It is established that heating up to 400° C can be considered the boundary of the structural integrity of concrete. The conditions for using the results of these studies in determining the values of a function that characterizes the change in the long-term strength of a material in the mechanics of heterogeneous structures are formulated. The function of the material destruction measure is introduced to describe the nature of the structural changes in the material at a given constant continuous load, and its change for different levels of a continuous load is considered.

Correlation between the Compressive, Tensile Strength of Old Concrete under Marine Environment and Prediction of Long-Term Strength

Compressive strength and tensile strength are important mechanical properties of concrete. The long-term strength of concrete under real service environment is an important parameter when evaluating existing buildings, which should also be properly considered in structural design. In this study, the relationship between compressive and splitting tensile strength of old concrete existing for long period under marine environment was investigated. At a deserted harbour, concrete cores samples were drilled by pairs in site. For each pair of samples, the two cores were drilled from the adjacent location and conducted to compressive, splitting tensile test, respectively. 48 compressive and splitting tensile strengths were finally obtained. From the test results, tensile strength presents general uptrend with compressive strength, and the two parameters are well positively correlated. Exponential model generally recommended by building codes or literatures is still capable of describing the relationship between compressive and tensile strength of old deteriorated concrete, when function parameters are properly determined. Based on statistical theory and the experimental result of this study, a method for predicting long-term tensile strength of concrete is developed and an example is given, which may provide a potential way to estimate long-term concrete strength under real marine environment.

Prediction of Long-Term Strength of Concrete Based on Artificial Neural Network

Recently, the safety of existing civil engineering structures attracts more and more attention. The long-term strength of concrete plays a key role during the assessment of safety and durability for civil engineering structures. The strength of concrete will gradually decrease during the service of civil engineering structures. It is significant to accurately predict the strength deterioration of concrete for correctly evaluating the safety of structures. The factors affecting the long-term strength of concrete include environment type, age, climate, water cement ratio, amount of cementing material and so on. In this paper, artificial neural network with powerful mapping ability has been selected to predict the long-term strength of concrete. First, there-layer BP neural network with age, water cement ratio, amount of cementing material as input and long-term strength as output was built. Then, the neural network was trained by the samples measured in real structures and the well-trained neural network was test. From the test results, the trained neural network can accurately predict the long-term strength of concrete with the error less then 9%.

Influence of initial curing temperature on the long-term strength of concrete

The growth of concrete strength is markedly influenced by curing temperature and age. In this paper, the reason why final strength difference occurs between concrete cured under various isothermal temperatures is analysed from a microreaction mechanism angle. Based on an available long-term strength predicting model, a modified model is proposed that could quantify the initial temperature's impact on the long-term and limiting strength. Moreover, experimental data available in the literature are collected and utilised to regress and confirm the parameter value in this new model. The results of analysis for the model indicate that the initial 4 h temperature determines concrete's final strength if neglecting other non-temperature factors.

THEORETICAL FOUNDATIONS FOR THE STUDY OF SEISMIC RESISTANCE OF BENT REINFORCED CONCRETE ELEMENTS

Abstract. This paper will focus on finding the seismic load based on a nonlinear deformation model of the bent reinforced concrete elements. The aim of this paper is to introduce the real characteristics of concrete and armature in practical calculations of finding the rigidity of bending elements and other elements of reinforced concrete structures and to study the effect of these deformational characteristics on the seismic resistance of reinforced concrete elements. The method of seismic resistance of the construction is chosen based on the rigidity of the elements of the construction. The novelty of this research work lies in the fact that a nonlinear deformational model of solid mechanics is used in order to find the rigidity of bent reinforced concrete elements. This paper provides numerical examples. The conclusion about a significant increase in seismic load was made based on the results of numerical examples, that are considering creep of concrete and longterm strength of concrete.

Some factors influencing the long term strength of concrete

Conventional creep and crushing tests are usually concerned with the effects of loadings which are applied during relatively short periods of a few minutes. However, gradual applications of the loading, especially during the initial stages, can produce increases in the ultimate strength of the concrete due to a form of solid body compaction which can the take place. The paper describes the increases in strength which have been obtained with mortars and concretes made with Thames Valley aggregates.