Nondestructive Determination of Strength of Concrete Incorporating Industrial Wastes as Partial Replacement for Fine Aggregate

Schmidt rebound hammer test was employed in this study as a nondestructive test. This test method has been universally utilized due to its non-destructiveness for quick and easy assessment of material strength properties and quality of concrete of an existing structure. Industrial waste materials (air-dried alum sludge, treated alum sludge, limestone dust and quarry dust) were employed as replacement material for fine aggregates in this study. A normal strength concrete was designed to achieve 35 MPa at 28 days, with industrial waste materials replacing fine aggregate at different percentages (0%, 5%, 10% and 15%), and then cured for 7, 28 and 180 days. The compressive strength values and rebound numbers for all the mixes obtained were correlated, and a regression equation was established between compressive strength and Schmidt rebound number. The correlation result showed an excellent relationship between rebound number and compressive strength of concrete produced in this study at all curing ages, with correlation coefficients of R2 = 0.98, R2 = 0.99 and R2 = 0.98. The predicted equation showed a strong relationship with the experimental compressive strength. Therefore, it can be used for the prediction of compressive strength of concrete with industrial waste as a replacement for fine aggregate.

Using of metakaolin to produce colored geopolymer concrete

This study was related to produce colored geopolymer concrete using metakaolin and adding two types of red (iron oxide) and green (chromium oxide) pigments with three additional ratios for each of the listed colors (0, 2, 4, 6 )% wt of metakaolin, and study some mechanical properties of colored geopolymer concrete. The experimental investigation has dealt with the fresh properties(slump) of the colored geopolymer concrete mixes as well as some of the mechanical properties of the hardened concrete by testing specimens in compressive strength, modulus of rupture, Rebound number (RN), and ultrasonic pulse velocity (UPV). Show us that (2% wt) pigment percentage gives the best results.

Experimental Study on Special Testing Strength Curve for Compressive Strength Evaluation by Rebound Method

This article aims to improve the accuracy and predictability of rebound method in compressive strength evaluation of concrete members of the Yanchong Expressway, which is an important traffic guarantee project for the 2022 Winter Olympics Games in Zhangjiakou city, Hebei Province, China. For this purpose, concrete specimens were prepared by the mixing ratios of C35, C40, and C50. First of all, the paper investigated the effects of curing age, types, and dosage of mineral admixtures (fly ash and slag) on concrete rebound number and compressive strength. Then, the special testing strength curves of 7 d and 90 d curing age were proposed. The results showed that the average relative errors of the special testing strength curves were reduced by 35.99% and 20.26% respectively, compared with the national testing strength curve. Fly ash and slag were beneficial to the growth of concrete rebound numbers but cannot contribute to the growth of concrete compressive strength (except for fly ash single-mixed with 15% dosage). The present results can provide a significant reference for the compressive strength evaluation and later maintenance of concrete members of the Yanchong Expressway or other projects with tight construction period in this area.

STUDYING SOME OF THE MECHANICAL AND PHYSICAL PROPERTIES OF COLORED GEOPOLYMER CONCRETE

This study has been done to study the physical and mechanical characteristics of colored geopolymer concrete by adding two types of pigments yellow (iron oxide hydroxide) and blue (cobalt) with three additional proportions for each of the listed colors (0,2, 4, 6% wt), some materials which are available in the native market and other materials imported from outside of the country. The experimental investigation has dealt with the fresh properties(slump) of the colored geopolymer concrete mixes as well as some of the mechanical and physical characteristics of the hardened concrete by testing specimens in compressive strength, flexural strength, water absorption, Rebound number (RN), and ultrasonic pulse velocity (UPV). In addition to that, Finding a relationship between the destructive (strength of compressive) and (RN and UPV) tests. Show us that (2% wt) pigment percentage gives the best results.

Comparison of Nondestructive Testing Method for Strength Prediction of Asphalt Concrete Material

Concrete is one of the most common construction materials used in rigid pavement, bridges, roads, highways, and buildings. Compressive strength is one of the most important properties of concrete, which determines its quality. This study aims to present the use of a new surface dielectric method to estimate concrete compressive strength. Six concrete mixtures were produced with compressive strengths ranging from 30 to 60 MPa. Compressive strength and strength development were determined during 28 days of curing. All concrete mixes were tested using the ASTM standard. The dielectric properties, ultrasound velocity, and rebound number of all concrete mixes were also measured at each day of curing. The results obtained from the proposed dielectric method in predicting the compressive strength of concrete were compared with the rebound hammer and ultrasonic velocity that are frequently used to evaluate the compressive strength of concrete. The dielectric method shows a higher square correlation coefficient than the other two methods. The results also indicate that combined more than one method of nondestructive techniques will lead to higher prediction and could help to reduce some errors associated with using a certain method alone. The result indicate that the finding of this study could lead to help in reducing the time of evaluating concrete during construction and could also provide tools for practicing engineer to take decision faster with more confidence level on quality of concrete. Doi: 10.28991/cej-2021-03091645 Full Text: PDF

The Behavior of Non-Destructive Test for Different Grade of Concrete

Rebound hammer tests are generally preferred as a non-destructive testing method as compared to destructive testing methods such as compression tests. In this study, a general series of rebound hammer tests and destructive tests were carried on in a heavy concrete laboratory. A set of concrete cubes measuring 100 x 100 x 100 mm were cast and subjected to water curing for 7, 14 and 28 days to obtain the cube strength and rebound number. Three grades of concrete, namely M20, M25 and M30 were used in this experiment. At 28 days, the minimum target strength should be 30 MPa. The rebound hammer tests were conducted before the compression tests. The data obtained for each test was evaluated and tabulated in the findings of this study. It was found that the variation between predicted strength and experimental strength for the rebound hammer test was 0.18%. This indicates that the rebound hammer test is able to predict strength with acceptable accuracy.

INFLUENCE OF WATER-CEMENT RATIO AND WATER REDUCING ADMIXTURES ON THE REBOUND NUMBER OF HARDENED CONCRETE

In this paper, effect of water-cement ratio (w/c) and type of water reducing admixtures (WRA) on the Schmidt hammer rebound number (RN) were investigated. Concrete of mix ratio 1:2:4 was prepared at the w/c of 0.45, 0.50, 0.55 and 0.60 and with each of the three WRA at the w/c of 0.45. Concrete cubes of size 150 mm were cast and cured in water for 3, 7 and 28 days. RNs of the cubes were determined and the compressive strengths (fc) corresponding to the RNs obtained from the conversion graph supplied by the manufacturer were compared with the compressive strengths obtained from crushing machine (CM). The results showed that as the w/c increased, the RN increased up to when w/c was 0.5 and began to drop, while there was no significant effect of all the WRA on the RN. It was also found that fc obtained from CM and those obtained using the conversion graph differed considerably. A new correlation graph was therefore proposed, which showed a correlation coefficient of 0.96, while coefficient of determination obtained for the regression equation between RN and fc, was as high as 0.92. The study concluded that w/c had effect on RN and that the equation developed could be used to determine fc, once RN is known.

Examining Hybrid and Single SVM Models with Different Kernels to Predict Rock Brittleness

The aim of this study was twofold: (1) to assess the performance accuracy of support vector machine (SVM) models with different kernels to predict rock brittleness and (2) compare the inputs’ importance in different SVM models. To this end, the authors developed eight SVM models with different kernel types, i.e., the radial basis function (RBF), the linear (LIN), the sigmoid (SIG), and the polynomial (POL). Four of these models were developed using only the SVM method, while the four other models were hybridized with a feature selection (FS) technique. The performance of each model was assessed using five performance indices and a simple ranking system. The results of this study show that the SVM models developed using the RBF kernel achieved the highest ranking values among single and hybrid models. Concerning the importance of variables for predicting the brittleness index (BI), the Schmidt hammer rebound number (Rn) was identified as the most important variable by the three single-based models, developed by POL, SIG, and LIN kernels. However, the single SVM model developed by RBF identified density as the most important input variable. Concerning the hybrid SVM models, three models that were developed using the RBF, POL, and SIG kernels identified the point load strength index as the most important input, while the model developed using the LIN identified the Rn as the most important input. All four single-based SVM models identified the p-wave velocity (Vp) as the least important input. Concerning the least important factors for predicting the BI of the rock in hybrid-based models, Vp was identified as the least important factor by FS-SVM-POL, FS-SVM-SIG, and FS-SVM-LIN, while the FS-SVM-RBF identified Rn as the least important input.

Relationship of Physical Properties of Limestone and Marble with Rock Strength Under Specific Geological Conditions from Khyber Region Hunza

The uniaxial compressive strength (UCS) is one of the input parameters mostly used in surface andunderground designs. A literature review revealed that most of the empirical equations between UCS and Schmidthammer rebound number (N) are not satisfactory because of the low coefficient of correlation. In most of the cases, asingle formula is used for all types of rocks. In this study, a relationship UCS with N, slake durability, moisture content,and specific gravity has been developed for a particular limestone and marble deposit. These equations help todetermine the strength of these deposits directly using N value and other properties. The UCS value increased withincreasing N value, specific gravity, and slake durability. While the UCS value decreased with increasing moisturecontent. A relation between slaking cycles and slake durability index is also developed. In this study, the slakedurability value decreased with increasing slaking cycles for both limestone and marble. The UCS showed a linearrelationship with these physical properties.

Relationship of Physical Properties of Limestone and Marble with Rock Strength Under Specific Geological Conditions from Khyber Region Hunza

The uniaxial compressive strength (UCS) is one of the input parameters mostly used in surface andunderground designs. A literature review revealed that most of the empirical equations between UCS and Schmidthammer rebound number (N) are not satisfactory because of the low coefficient of correlation. In most of the cases, asingle formula is used for all types of rocks. In this study, a relationship UCS with N, slake durability, moisture content,and specific gravity has been developed for a particular limestone and marble deposit. These equations help todetermine the strength of these deposits directly using N value and other properties. The UCS value increased withincreasing N value, specific gravity, and slake durability. While the UCS value decreased with increasing moisturecontent. A relation between slaking cycles and slake durability index is also developed. In this study, the slakedurability value decreased with increasing slaking cycles for both limestone and marble. The UCS showed a linearrelationship with these physical properties.