Splitting Strength Of Concrete Research Articles

Predicting the impact of adding metakaolin on the splitting strength of concrete using ensemble ML classification and symbolic regression techniques –a comparative study

The mechanical characteristics of concrete are crucial factors in structural design standards especially in concrete technology. Employing reliable prediction models for concrete’s mechanical properties can reduce the number of necessary laboratory trials, checks and experiments to obtain valuable representative design data, thus saving both time and resources. Metakaolin (MK) is commonly utilized as a supplementary replacement for Portland cement in sustainable concrete production due to its technical and environmental benefits towards net-zero goals of the United Nations Sustainable Development Goals (UNSDGs). In this research work, 204 data entries from concrete mixes produced with the addition of metakaolin (MK) were collected and analyzed using eight (8) ensemble machine learning tools and one (1) symbolic regression technique. The application of multiple machine learning protocols such as the ensemble group and the symbolic regression techniques have not been presented in any previous research work on the modeling of splitting tensile strength of MK mixed concrete. The data was partitioned and applied according to standard conditions. Lastly, some selected performance evaluation indices were used to test the models’ accuracy in predicting the splitting strength (Fsp) of the studied MK-mixed concrete. At the end, results show that the k-nearest neighbor (KNN) outperformed the other techniques in the ensemble group with the following indices; SSE of 4% and 1%, MAE of 0.1 and 0.2 MPa, MSE of 0, RMSE of 0.1 and 0.2 MPa, Error of 0.04% and 0.04%, Accuracy of 0.96 and 0.96 and R2 of 0.98 and 0.98 for the training and validation models, respectively. This is followed closely by the support vector machine (SVM) with the following indices; SSE of 7% and 3%, MAE of 0.2 and 0.2 MPa, MSE of 0.0 and 0.1 MPa, RMSE of 0.2 and 0.3 MPa, Error of 0.05% and 0.06%, Accuracy of 0.95 and 0.94, and R2 of 0.96 and 0.95, for the training and validation models, respectively. The third model in the superiority rank is the CN2 with the following performance indices; SSE of 15% and 4%, MAE of 0.2 and 0.2 MPa, MSE of 0.1 and 0.1 MPa, RMSE of 0.3 and 0.3 MPa, Error of 0.08% and 0.07%, Accuracy of 0.92 and 0.93 and R2 of 0.92 and 0.93, for the training and validation models, respectively. These models outperformed the models utilized on the MK-mixed concrete found in the literature, therefore are the better decisive modes for the prediction of the splitting strength (Fsp) of the studied MK-mixed concrete with 204 mix data entries. Conversely, the NB and SGD produced unacceptable model performances, however, this is true for the modeled database collected for the MK-mixed Fsp. The RSM model also produced superior performance with an accuracy of over 95% and adequate precision of more than 27. Overall, the KNN, SVM, CN2 and RSM have shown to possess the potential to predict the MK-mixed Fsp for structural concrete designs and production.

Effect of high temperature on residual splitting strength of desert sand concrete

AbstractThe ordinary medium sand can no longer meet the increasing demands of engineering projects. Construction costs can be reduced and the natural environment can be protected by rational use of the local desert sand. To evaluate the spalling and fire resistance of the concrete, the desert sand concrete (DSC) is heated to 100–800°C and then cooled for splitting tensile strength test. The test results indicate that with the increment of desert sand replacement rate (DSRR), the compressive strength of DSC increases first and then decreases. The maximum value is reached when DSRR is up to 40%. The presence of fly ash slows down the loss of splitting strength of concrete with the temperature increasing. The regression model is established to predict the functional relationship between the concrete splitting strength and temperatures under heating and air cooling conditions. The result shows that the predictions calculated by the formula are consistent with the experimental results. The formula can be employed as a constitutive relation of the computer model to evaluate the spalling and fire resistance of the DSC structure.

Improving mechanical properties of manufactured sand concrete with high biotite content: Application of magnetic separation process and equipment optimization

• Degradation mechanism of biotite in manufactured sand on concrete performance was presented. • An empirical formula of compressive strength for different biotite content was presented. • FEM-DEM coupling program was developed to optimize biotite separation process. Harmful components such as biotite in fine aggregates formed by natural rock crushing need to be rigorously assessed and effectively separated to reduce their potential damage to concrete structures. In this study, magnetic separation was used to remove excess biotite from manufactured sand and to realize the upgrade of manufactured sand, and a series of laboratory tests were carried out to study the influences of biotite content on the compressive strength and splitting strength of concrete. Experimental results show that the magnetic separation method can effectively reduce the biotite content in concrete from 10 % to 2 %, thus improving the mechanical properties of concrete. Through microscopic characterization, we found that the surface layer of biotite had a strong bonding effect with the early hydration product. This bonding effect contributes to the early strength of concrete, leading to a small difference in the strength values of manufactured sand concrete with different biotite contents. With increasing curing age, the strength contribution caused by this bonding effect gradually decreases. In addition, FEM-DEM coupling simulation was used to optimize the operation parameters and magnetic system structure of the magnetic separator to further achieve efficient separation of biotite from manufactured sand. Numerical prediction indicates that the dry magnetic separator has an extrusion magnetic system structure, which makes the magnetic induction and magnetic induction gradient at the guide disk higher and provides a much greater magnetic force than other competitive forces for biotite particles. To efficiently recover low-grade manufactured sand (low biotite content) from manufactured sand, the feed rate t , conveyor belt speed V and magnet-to-steel disk thickness ratio μ should be kept at 0.8 kg/s, 0.85 m/s and 3, respectively. This study can provide potential solutions and broad application value for the problem of manufactured sand with high biotite content in practical engineering.

Effect of Temperature on Properties of Concrete in Stirring Process

Taking composite silicate concrete as the research object, the double horizontal shaft mixing method is used to mix concrete. The setting time, strength and workability tests are carried out to study the influence of temperature on the mechanical properties of concrete in the ordinary mixing process. The results show that the temperature has great influence on the setting time, compressive strength and splitting strength of concrete. Reasonable control of cement temperature has important guiding significance and theoretical basis in practical construction application.

Energy Absorption Characteristics of PVC Coarse Aggregate Concrete under Impact Load

In this paper, polyvinyl chloride (PVC) coarse aggregate with different mixing contents is used to solve the problems of plastic pollution, low energy absorption capacity and poor damage integrity, which provides an important reference for PVC plastic concrete used in the initial support structures of highway tunnels and coal mine roadway. At the same time, the energy absorption characteristics and their relationship under different impact loads are studied, which provides an important reference for predicting the energy absorption characteristics of concrete under other PVC aggregate content or higher impact speed. This study replaced natural coarse aggregate in concrete with different contents and equal volume of well-graded flaky PVC particles obtained by crushing PVC soft board. Also, slump, compression, and splitting strength tests, a free falling low-speed impact test of steel balls and a high-speed impact compression test of split Hopkinson pressure bar (SHPB) were carried out. Results demonstrate that the static and dynamic compressive strength decreases substantially, and the elastic modulus and slump decrease slowly with the increase of the mixing amount of PVC aggregate (0–30%). However, the energy absorption rate under low-speed impact and the specific energy absorption per MPa under high-speed impact increase obviously, indicating that the energy absorption capacity is significantly enhanced. Regardless of the mixing amount of PVC aggregate, greater strain rate can significantly enhance the dynamic compressive strength and the specific energy absorption per MPa. After the uniaxial compression test or the SHPB impact test, the relative integrity of the specimen is positively correlated with the mixing amount of PVC aggregate. In addition, the specimens are seriously damaged with the increase of the impact strain rate. When the PVC aggregate content is 20%, the compressive strength and splitting strength of concrete are 33.8 MPa and 3.26 MPa, respectively, the slump is 165 mm, the energy absorption rate under low-speed impact is 89.5%, the dynamic compressive strength under 0.65 Mpa impact air pressure is 58.77 mpa, and the specific energy absorption value per MPa is 13.33, which meets the requirements of shotcrete used in tunnel, roadway support and other impact loads. There is a linear relationship between the energy absorption characteristics under low-speed impact and high-speed impact. The greater the impact pressure, the larger the slope of the fitting straight line. The slope and intercept of the fitting line also show a good linear relationship with the increase of impact pressure. The conclusions can be used to predict the energy absorption characteristics under different PVC aggregate content or higher-speed impact pressure, which can provide important reference for safer, more economical, and environmental protection engineering structure design.

Prediction on concrete splitting strength from compressive strength of drilling‐core

AbstractCores were drilled from the panels made of different concrete mixtures. The compressive strength and splitting strength of core and cube specimens were tested at the ages of 7, 28, 60, 90, and 180 days. The effect of the diameter on concrete core splitting strength was examined. The strength correction factors were determined to convert the splitting strength of the core with diameter of 75 mm to that of the core with diameter of 100 mm. The regression analysis was carried out using experimental data to evaluate the core splitting strength as a function of the compressive strength of the concrete core. Then, the reliability of the proposed equation based on experimental data for compressive strength ranging from 20 to 80 MPa was assessed with the integral absolute error (IAE). Other existing relations between splitting strength and compressive strength of the cylinder were also evaluated with IAE, and most of the existing relations are not suitable for splitting strength of cores. The accurate power function relation formula is obtained with the test data. Only compressive test can be carried out by using drilling core samples in existing buildings, and the compressive strength and tensile strength of concrete can be obtained simultaneously, thus the numbers of splitting tests can be reduced and the mechanical property of existing buildings can be evaluated.

Mechanical Properties of Class C High Volume Fly Ash Concrete with Lime Water as Mixing Water

This paper reports an investigation on mechanical properties of high volume fly ash (HVFA) concrete produced using different types of mixing water i.e. tap water and saturated lime water. The mechanical properties of ordinary Portland cement concrete are also investigated as control tests. The concrete were tested for their compressive strength, flexural strength and splitting tensile strength at the curing ages of 56 days. The results showed that strength development of high volume fly ash concrete up to 56 days is lower than ordinary portal cement. In addition, the flexural strength and splitting strength of concrete are lower than ordinary Portland cement. Moreover, the use of saturated lime water as mixing water reduces the mechanical properties of class C high volume fly ash concrete.

Experimental Research about the Effect on Bond Properties between Ceramsite Concrete and Reinforcement with Age

After the pilot study about different-aged ceramsite concrete specimens, the curve and the formula about the ceramsite concrete splitting strength with age developing are obtained, the curve and the formula about the relative bond strength with age are analyzed, it provides a theoretical basis for the project production of ceramsite concrete practice.

Experiment Study on the Frost Resistance of Steel Fiber Reinforced Concrete

In order to study various factor affecting durability of steel fiber reinforced concrete (SFRC), basic experimental research that combine the action of freezing-thawing cycles and deicing salt to SFRC was conducted. In the experiment, the volume fraction of steel fiber and number of freeze-thaw circulation are taken as variable parameter. Based on the different numbers of freeze-thaw circulation, weight losing of SFRC, splitting strength and the dynamic modulus of elasticity were measured. Furthermore, the reinforced mechanism of the SFRC under the action of freeze-thaw was analysed. The test results show that after adding a certain amount of steel fiber to the concrete, cracks in concrete at early stage are effectively prevented and the permeability of concrete is obviously reduced, thus the durability of concrete is improved. The reinforced actions of steel fiber on splitting strength of concrete are notable and the influence of steel fiber volume fraction on the frost-resisting property is obvious. On the contrary, the negative effects of steel fiber with high volume fraction on the splitting strength of concrete exist. The best performance of SFRC can be got when the steel fiber quantity is 1.5%.