Journal of Civil Engineering and Materials Application
Volume:8 Issue: 2, Spring 2024

Assessment of concrete compressive strength is important in ensuring structural integrity and durability of concrete structures. Traditionally, destructive testing methods using compression machines have been the standard for determining concrete strength. However, advancements in technology have introduced non-destructive testing methods such as the rebound hammer, which offer quick and economical alternatives. This study was aimed at comparing the accuracy, reliability, and practicality of these two methods in assessing concrete compressive strength. The experimental investigation involved conducting tests on concrete specimens using both the rebound hammer and compression machine. Data on rebound values and compressive strength measurements were collected and analysed using statistical approaches to evaluate the correlation between results obtained from these two methods. Factors such as surface conditions and moisture content were considered in the analysis to understand potential influences on test outcomes.Results from the research indicated strong correlations between compressive strength values obtained using the rebound hammer and compression machine tests. The comparative analysis highlighted scenarios where methods have very strong correlations and thus more likely to give comparable results. The findings of this research also offer insights that can enhance the reliability and accuracy of assessing concrete compressive strength on construction projects.

Shells are the most widely used structural elements forming roofs of buildings and other structures for supporting loads to its surface. There are many types of shell forms that can be made and practical. The most common shell form is a cylindrical shell. In general, it can be said that the shell is a curved surface whose thickness is insignificant compared to its radius and other dimensions. There are various theories for the analysis of shell structures. How to apply each of these theories depends on the geometric shape, shell material, shell application and boundary conditions as well as applied loads. Researchers have searched for information about the analysis methods of shell structures using various methods. Some used experimental methods for shell structures while others used analytical methods. This is an evaluation of these methods. In this paper we will research some historical aspects of development of the theory of shells as well as their recent developments. A survey and introducing of the books and articles of methods of shells analysis have been discussed in this article.

Ever since their introduction nearly a century ago, concrete paving blocks have become increasingly common. They evolved into an alternative to burned clay brick and natural stone. Concrete paving blocks are used to lay down areas for vehicles and pedestrians as well. Durability is one of the most crucial elements in the production of high-quality concrete paving blocks. The aim of this study is to optimize the mechanical properties of concrete paving block units by experimenting with different admixtures. Compressive strength, water absorption, oven dry density, and drying shrinkage are among the attributes that were evaluated. The cost of production was also contrasted with and without the use of an admixture to achieve a comparable compressive strength. The results showed that admixtures could be used to produce high early strength units, and this was considered to be an economical factor in the production of concrete paving block units. At all ages, the use of admixtures increased these units' compressive strength by 30–40%. Although they did slightly increase density, additives also decreased the absorption and drying shrinkage of concrete paving block units.

Pavements are part of the most important structure of the roads and a huge amount of money is spent on their repair and improvement every year. If special measures are used in the mixing plan of these procedures, most of which are made of asphalt mixtures, millions of dollars can be saved annually. On the other hand, in recent years, in addition to paying attention to increasing the life of asphalt mixtures, special attention has been paid to the use of recycled materials and materials to improve the life of asphalt pavements, because this work has environmental advantages in addition to economic benefits. Therefore, in this research, the cracking resistance of asphalt mixtures containing two recycled materials, steel slag and rubber powder has been investigated. Cracking resistance has been investigated using fracture toughness in two loading modes, one and two pure, at two low temperatures of -12 and -24. The results of this research showed that the use of steel slag (50 and 100 percent) and rubber powder (5 and 10 percent) can be investigated and loaded in both cases to improve the fracture toughness of asphalt mixtures. Meanwhile, the combination of both modifiers in the percentage of 5% of rubber powder and 50% of steel slag provides the most optimal amount possible.

This study, after modeling three types of 3, 5 and 8-story frames with 2, 3 and 4 spans by Sap2000 using two categories of earthquake records of far and near-field for different levels of PGA, the process of forming plastic hinges has been investigated and evaluated by performing nonlinear time history analysis. The obtained results showed that the first plastic hinges were formed in the 3-story frames in the lower stories and in the case of the 5 and 8-story frames in the middle stories. furthermore, the frequency corresponding to the formation of the first collapse prevention (CP) hinge in the case of the 3-story frame with 2, 3, and 4 span is equal to 1.11, 1.31, and 1.22 Hz, in the case of the 5-story frame it is equal to 0.85, 1.03, and 0.94 Hz, and in the case of the 8-story frame it is equal to 0.44, 0.42, and 0.4 Hz, respectively. Other results showed that the behavior of 3-story frames under the effect of far-field records and the behavior of 5 and 8-story frames under the effect of near-field records are in higher dynamic instability conditions. Also, with the increase of spans and the number of floors, the possibility of damage and dynamic instability in the frames has increased. For all frames with different story numbers, by increasing the number of spans from 2 to 4, an increase of 5.88, 22.4 and 38.3% has been obtained respectively in the number of hinges formed in the frame.