Flexural strength compressive strength converter

In some instances, splitting tensile strength of cores by ASTM C is used, but experience is limited on how to apply the data. Flexural tests are extremely sensitive to specimen preparation, handling, and curing procedure. Beams are very heavy and can be damaged when handled and transported from the jobsite to the lab. Allowing a beam to dry will yield lower strengths.

Beams must be cured in a standard manner, and tested while wet. Meeting all these requirements on a jobsite is extremely difficult, often resulting in unreliable and generally low MR values. A short period of drying can produce a sharp drop in flexural strength.

Many state highway agencies have used flexural strength, but are now changing to compressive strength or maturity concepts for job control and quality assurance of concrete paving. The data point to a need for a review of current testing procedures. They also suggest that, while the flexural strength test is a useful tool in research and in laboratory evaluation of concrete ingredients and proportions, it is too sensitive to testing variations to be usable as a basis for the acceptance or rejection of concrete in the field Reference 3.

ACI Committees and on concrete pavement construction and design and the Portland Cement Association PCA point to the use of compressive strength tests as more convenient and reliable. The concrete industry and inspection and testing agencies are much more familiar with traditional cylinder compression tests for control and acceptance of concrete.

The tensile strength is the key index in structural design. Thus it is important to establish the relationship between the compressive and the splitting tensile strength for SAP concrete. The relationship between splitting tensile strength and compressive strength of ordinary concrete as proposed by American Concrete Institution ACI American Committee Institute, is as follows Eq. According to the model code of the International Federation for Structural Concrete International Federation for Structural Concrete, CEB-FIP , the relationship between splitting tensile strength and compressive strength of ordinary concrete is defined as:.

Based on the recommended equations between the splitting tensile strength and compressive strength in the design codes of the various countries, it can be found that the power function is widely used to describe the relationship between the two variables.

This fact demonstrates that, as the compressive strength of concrete increases, the growth rate of the splitting tensile strength gradually slows down. Besides, since concrete is a brittle material, the growth of splitting tensile strength has certain limitations.

The test data and the fitting curve are plotted in Figure 4. The recommended equation is closest to the European specifications. In general, as mentioned above, SAP concrete has a higher splitting tensile strength than ordinary concrete, and this is a valuable factor in practical engineering application. The relationship of cubic compressive strength and splitting tensile strength of SAP concrete. For the relationship of flexural strength and compressive strength of ordinary concrete, the following expression is proposed in ACI American Committee Institute, The flexural strength of ordinary concrete f f can be calculated from f c u.

Besides, most of the national standards have established a linear relationship between the two parameters the rate is referred to as quasi flexure-compression ratio. Table 5 shows the calculation of the quasi flexure-compression ratios of the different SAP concretes.

According to the calculation results, SAP concrete has various features from ordinary concrete. Thus, the relationship between compressive strength and flexural strength of SAP concrete should depend on the incorporated SAP content expressed by the internal curing water-cement ratio in this paper. Guo carried out uniaxial compressive and four-point bending tests for SAP concrete with an effective water-cement ratio of 0.

The internal curing water-cement ratio was 0—0. Zhang carried out uniaxial compressive and four-point bending tests for SAP concrete with an effective water-cement ratio of 0.

The cubic compressive strength and flexural strength of concrete with different SAP contents were obtained in the research. All SAP used in their experiments were chemical polymers, and the effective water-cement ratio was similar to that in this paper.

By integrating the data of Guo , and Zhang on the strength of SAP concrete and incorporating the regression analysis with the data in this article, a more applicable equation can be obtained. Referring to the rational form proposed by Xiao and Li , the relationship equation between SAP concrete strength at different internal water-water-cement ratios is:.

After the fitting analysis, the relationship between the flexural strength and compressive strength can be calculated as follows:. The combined plot of test data and the fitting curve is shown in Figure. In Figure 5 , it is clear that, when the internal curing water-cement ratio is small, the quasi flexure-compression ratio of SAP concrete remains nearly constant which is similar to the performance of ordinary concrete.

After the internal curing water-cement ratio increases to 0. Moreover, at an internal curing water-cement ratio higher than 0. The negative influence will continue to increase as the SAP content increases. To compare the effect of different regression curves when negligible SAP concentration in concrete, the following quadratic polynomial equation is also proposed:.

Besides, when the internal curing water-cement ratio is low, the fitting curve 1 rational form remains relatively stable and rapidly decreases when the value of the internal water-cement ratio increases. This phenomenon indicates that Eq. The splitting tensile strength and flexural strength reflect the tensile properties of concrete, although these two strengths are different. There has a long-established concern that the splitting tensile strength is closer to the real tensile strength in a material.

The experimental data show that the flexural strength often tends to be higher than the splitting tensile strength for the mutual restraint of longitudinal fibers in the tensile zone which increases the material tensile strength at the four-point bending tests Zheng et al. The Chinese codes generally use splitting tensile strength instead of the flexural strength to present the axial tensile strength of concrete.

However, due to the addition of SAP and internal curing water, the reduction rate of the flexural strength and splitting tensile strength of SAP concrete varies.

Therefore, in SAP concrete, the conversion equation between these two strengths need to be further studied. The relationship between flexural strength and splitting tensile strength of ordinary concrete as proposed by the American Concrete Institution ACI American Committee Institute, is:.

According to the experimental data of the flexural strength and the splitting tensile strength, the relationship is fitted by the linear model:. These different specifications equations and the fitting Eq. Under the same splitting tensile strength, the flexural strength of SAP concrete obtained in the test is significantly lower than the normal concrete calculated by different national specifications.

However, it is close to the results of ordinary concrete in ACI The relationship between the splitting tensile strength and flexural strength. These results are consistent with the different loss rates of the flexural strength and splitting tensile strength in this study. Compared with ordinary concrete, the SAP concrete has a greater loss in flexural strength, especially when the internal curing water-cement ratio was high.

It can be attributed to the formation of small voids in the concrete after SAP gradually releases the internal curing water, thus weakening the concrete section. Nevertheless, due to the adhesive effect of SAP film, the decrease rate in splitting tensile strength was lower than in the flexural strength.

Therefore, in practical engineering applications, it is important to focus on the flexural strength of SAP concrete, which can be more degraded than the splitting tensile strength. Considering only the splitting tensile strength of SAP concrete may lead to unsafe designs.

This paper studied the influence of SAP on the mechanical strengths of concrete and proposed the conversion equations among the splitting tensile strength, cubic compressive strength, and flexural strength of SAP concrete, which provided a reference for the practical engineering application of SAP concrete.

For the similar SAP utilized in this study, and concrete with an effective water-cement ratio of concrete between 0. Sequentially, as the content of SAP grows lager, the compressive strength decreases the fastest, followed by the flexural strength, and the splitting tensile strength is the slowest. When the internal curing water-cement ratio lower than 0.

As the internal curing water-cement ratio rises to 0. The proposed equation reflects the relationship between the flexural strength and the compressive strength of SAP concrete correctly.

Compared with the recommended equations by the global specifications, the flexural strength under the same splitting tensile strength of SAP concrete is lower. Calculating the flexural performance of SAP concrete from current specifications might lead to an overestimation of the flexural strength.

The weakening of the flexural strength exhibited in SAP concrete needs to be considered to obtain a safe design. FX initialized the idea of the study and wrote the manuscript. DC carried out the experiment and analyze the data.

CZ complemented the experiments and the experimental data. JR provided the necessary resources. The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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Download references. The authors also thank Associate Mrs. Tong Zhang for revising and proofreading this manuscript. You can also search for this author in PubMed Google Scholar. Correspondence to Xiamin Hu. We declare that we have no conflicts of interest to this work.

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Received : 27 December Accepted : 13 November Published : 23 November