Development of a method and a device for measuring the setting time of concrete

• Main Authors: Chih-Chieh Chan, 詹智捷
• Other Authors: Yiching Lin
• Format: Others
• Language: zh-TW
• Published: 2019
• Online Access: http://ndltd.ncl.edu.tw/handle/9ru454

博士 === 國立中興大學 === 土木工程學系所 === 107 === This study is mainly to develop a simple mechanical method for determination of the setting time of concrete. The method performs the flexural test on a PVC pipe filled with cement mortar/concrete. In the flexural test, the loading and unloading process with a certain external force is executed on the specimen at a fixed time interval to observe the change in flexural strain during condensation. The flexural strain is controlled within the linear elastic range, so that the specimen can be repeatedly loaded and unloaded, which belongs to a non-destructive test technology. This study first monitors the flexural strain of PVC pipes as a reference for the properties of PVC pipes. Subsequently, the flexural strain response over time was monitored to investigate the setting process of cement-based materials so as to estimate the initial and final setting time. The estimated setting time of mortar could be compared with that determined by the penetration resistance method (ASTM C403). Then, the difference in the setting time between concrete and the mortar sieved from concrete is discussed. Finally, the influence of the addition of Pozzolanic materials on concrete setting time is investigated. The experimental results show that the strain response of the PVC pipe and mortar can be divided into two stages. The first stage is that the cement mortar has not yet become plastic, and the flexural stress is mainly borne by the PVC pipe. The second stage is that the mortar has become plastic and gradually rigid and has the ability to bear the flexural stress so that the strain of the PVC pipe decreases with time. Both the initial and final setting times of mortar obtained from the flexural test were in good agreement with those determined by the penetration resistance method. In addition, two kinds of specimens were made to investigate their setting time. The fresh cement mortar was added with the saturated surface dry coarse aggregate to form concrete as the first kind specimen. The second kind specimen was made by removing the coarse aggregate larger than #4 sieve to form mortar. The test results show that the effect of the two kind specimens on the hydration reaction rate is very small and almost negligible. The flexural test method proposed in this study can be used to determine the setting time of cement materials, and the flexural test can be directly applied to the measurement of the setting time of concrete without the need to remove coarse aggregates larger than #4 in advance.