Evaluation on Early Strength Development of Concrete Mixed with Non-Sintered Hwangto Using Ultrasonic Pulse Velocity

Abstract

Currently, in order to reduce the greenhouse gases of global warming, research on alternative cement materials is being actively conducted in the construction industry to reduce cement use, and it is judged to be important to evaluate the timing of form removal for the initial age. Therefore, in this study, we evaluated the initial mechanical properties of concrete in which cement was partially replaced with non-sintered hwangto (NHT). Specimens without NHT (namely, normal mortar (NM) and normal concrete (NC)) and specimens with NHT (namely, non-sintered hwangto mortar (HTM) and non-sintered hwangto concrete (HTC)) were prepared. NHT was substituted for 15% and 30% of cement. Two water-to-binder (W/B) ratios, 41% and 33%, were used to analyze the variation in the mechanical properties according to the cement and NHT content per unit volume of concrete. The compressive strength and ultrasonic pulse velocity (UPV) were measured. Experimental results indicated that compressive strength decreased with an increase in NHT content. The mortar with NHT substitution rates of 15% and 30% exhibited higher UPV than NM at a W/B ratio of 41%, in contrast to the behavior observed for concrete. The UPVs of most specimens were similar regardless of the NHT substitution rate. The correlation between the compressive strength and UPV of HTC was analyzed, and therefrom, exponential equations with a high correlation coefficient (R2) were proposed for strength prediction; the resulting predictions were compared with the results of previous compressive strength prediction models.

Statistical Reliability Analysis of Ultrasonic Velocity Method for Predicting Residual Strength of High-Strength Concrete under High-Temperature Conditions

“…The early age model is used to evaluate the strength of concrete at an early age using UPV and to nondestructively gauge the time of vertical formwork demolding in the construction stage. To develop an early age model, researchers evaluated the compressive strength and UPV of concrete 24 h after concrete mixing and performed a regression analysis on the data, ultimately proposing a general exponential model [ 6 , 17 ].…”

“…Previous studies tested the statistical significance of the strength and UPV of heated and unheated concrete, and the results of the regression analysis were evaluated [ 21 ]. Concrete with a high-temperature history in the same UPV range showed a relatively high prediction rate in terms of compressive strength, and it was reported that crack formation owing to differences in the thermal expansion properties of mixed materials and voids owing to chemical decomposition contributed to the very low UPV [ 17 , 22 ]. Studies on the prediction of the strength of concrete at an early age using UPV have reported very low values, showing a different trend from the aforementioned research.…”

Strength Prediction of Non-Sintered Hwangto-Substituted Concrete Using the Ultrasonic Velocity Method

“…Among the non-destructive techniques employed for estimating compressive strength, the use of ultrasonic pulse velocity (UPV), which employs ultrasonic waves, has gained prominence. Consequently, numerous researchers are employing UPV to evaluate the mechanical properties or quality of concrete [ 20 , 21 , 22 ]. However, in the context of NSHC, additional research and analysis are required due to the lack of extensive experimentation.…”

Review of Residual Mechanical Properties of Concrete Mixed with Different Admixtures at High Temperatures

“…Thus, changes in the chemical and mechanical properties of concrete exposed to high temperatures have continuously drawn attention.Recently, in response to global warming, various efforts have been made to reduce emissions from the cement manufacturing process, which involves high carbon dioxide emissions. Studies have been conducted on the utilization of industrial byproducts or solid waste as replacement materials for cement [4][5][6]. As for the replacement materials, several studies have investigated fly ash (FA), ground granulated blast furnace slag (GGBFS), and metakaolin (MK) as admixtures [7][8][9].…”