Abstract
Healthy reinforced concrete should be highly alkaline to safeguard the passive protective film for reinforcement of steel bars against corrosion. pH measurement is gaining importance in research of cement-based materials (CBMs), such as paste, mortar and concrete, as well as in structural health monitoring and forensic engineering applications. However, insufficient information is available regarding the most practical, economical and applicable quantitative pH measurement method for CBMs from the sampling to measurement stage. Existing recommended methods for measuring pH have many variables that need to be investigated to determine how they influence the pH value. Samples were recommended to be ground into very fine particles for pH measurement. Preparing very fine particles of CBMs is costly and time consuming, while larger particles, with sizes similar to sand particles, are easier to obtain, without needing special equipment. This study aims to investigate the effect of different particle sizes on the pH of cement mortar. Mortar specimens were crushed and sieved to obtain different ranges of particle sizes to measure the pH values. Results showed that specimens with large particle sizes (between 600 µm and 4.75 mm) can produce similar results to specimens with very fine particle sizes (<600 µm) by increasing the solid-to-solvent ratio or the leaching time.
Highlights
Published: 29 August 2021Calcium silicates (C3 S and C2 S) are the main cementitious compounds in cement
Similar studies were conducted on concrete and paste materials [13,19,25,26], and the results revealed that large particles had lower pH than very fine particles
Ordinary Portland Cement (OPC) Type I (Tasek Corporation Berhad, Ipoh, Malaysia according to MS522 specification), local mining sand with a maximum grain size of 4.75 mm in saturated-surface-dry (SSD)
Summary
Published: 29 August 2021Calcium silicates (C3 S and C2 S) are the main cementitious compounds in cement. The high pH of concrete will enable the formation of a passive protective film on the embedded steel This thin oxide layer formed on the steel can prevent the metal atoms from dissolving and reduce the corrosion rate to an insignificant level [3]. Phenolphthalein solution is typically used as an indicator to test the depth of carbonation from the concrete surface because it changes from pink to colourless when the pH is less than 9.5 [6]. This method is not accurate enough to evaluate the durability of reinforced concrete, where the pH near the embedded steel is more than
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