MAT-742: EFFECT OF SUPPLEMENTARY CEMENTITIOUS MATERIALS ON THE RESISTANCE OF MORTAR TO PHYSICAL SULFATE SALT ATTACK

Physical sulfate salt attack is one of the most rapid and severe deterioration mechanisms in concrete structures. One of the most common approaches to improve resistance of concrete to sulfate attack is to use supplementary cementitious materials. However, physical salt attack may still cause damage to concrete with supplementary cementitious materials. Moreover, according to some literature sources, some supplementary cementitious materials may even reduce resistance to physical salt attack. The current research investigates the effect of supplementary cementitious materials on the ability of mortars to resist physical sulfate salt attack and its relationship with pore structure and transport properties. Mortar specimens with 45 and 65% replacement of cement by ground-granulated blast-furnace slag and with 20 and 40% replacement of cement by fly ash were exposed to physical sulfate attack. The results show a good correlation between the pore microstructure and transport properties to the resistance to physical salt attack. Ground-granulated blast-furnace slag was found to improve the resistance to physical salt attack, while fly ash demonstrated a negative effect

Quantification of Residual Unhydrated Cement Content in Cement Pastes as a Potential for Recovery

All types of concrete contain residual unhydrated cement. For example, unhydrated cement is present in high-strength concrete due to low water/cement ratios, as well as in old concrete due to coarser cement used in the past, and in fresh concrete waste due to the lack of curing. These residues of unhydrated cement are a waste of resources with potential for recovery and reuse. In this work, X-ray diffraction, thermogravimetric analysis, and analytical modeling were used to quantify the residual cement and the hydration degree of various cement pastes to explore their recovery potential. The study included cement pastes with water/cement ratios of 0.2–0.6 and residual unhydrated cement was found to be in the range 6–36%, indicating great potential for recovery and further use in the manufacture of new concrete

Effect of sulfates on hydration and properties of belite-rich cement paste

It is common practice to use gypsum in cement production to control setting time. Traditionally it is believed that sulfate from gypsum combines with aluminates to form ettringite and monosulfate to prevent flash set. However, previous studies have confirmed that sulfates also affect the hydration and mechanical properties of pure alite paste. In view of recent research and development of cements with a low carbon footprint that are rich in belite, the question about the effect of sulfate on hydration and mechanical properties of belite arises. Moreover, this question becomes even more relevant considering the use of raw materials and fuels containing high content of sulfate-bearing impurities. In this work, the influence of the sulfate content on the hydration of belite-rich cement was studied by means of isothermal calorimetry and X-ray diffraction. The effect of sulfate content on compressive strength was also investigated. In the course of this study, an increase in hydration degree of belite with an increase of sulfate content in cement was observed. The compressive strength also increased with the addition of sulfate. The increase in hydration degree of belite and compressive strength of belite-rich paste was associated with the incorporation of sulfate in the cementitious gel as opposed to the ettringite formation

A Comparative Study of Factors Influencing Hydration Stoppage of Hardened Cement Paste

There is no consensus on which hydration stoppage method is optimal to preserve the microstructure and mineral composition of samples, especially considering the specific aspects of different testing methods, such as TGA, MIP, or XRD. This paper presents a quantitative comparison between the most popular hydration stoppage strategies and parameters such as the sample piece size, the soaking time in a solvent, and the type, as examined on cement paste hydrated for 7 days. It was found that the carbonation appears either for samples smaller than 2.36 mm and bigger than 4.75 mm or samples soaked in a solvent for longer than 1 h. Fast solvent replacement leads to ettringite diminution and total pore volume increase. Among others, solvent replacement with subsequent gentle heating under a vacuum was found to be the most efficient, whereas it was experimentally demonstrated that isopropyl alcohol stops hydration faster than ethanol and acetone

Effect of internal curing by using superabsorbent polymers (SAP) on autogenous shrinkage and other properties of a high-performance fine-grained concrete: results of a RILEM round-robin test

The article presents the results of a round-robin test performed by 13 international research groups (representing fifteen institutions) in the framework of the activities of the RILEM Technical Committee 225-SAP "Applications of Superabsorbent Polymers in Concrete Construction". Two commercially available SAP materials were used for internal curing of a high-performance, fine-grained concrete in combination with the addition of extra water. The concrete had the same mix composition in all laboratories involved but was composed of local materials. All found a considerable decrease in autogenous shrinkage attributable to internal curing. Also, with regard to the shrinkage-mitigating effect of both particular SAP materials, the results were consistent. This demonstrates that internal curing using SAP is a robust approach, working independently of some variations in the concretes' raw materials, production process, or measuring technique. Furthermore, the effects of internal curing on other properties of concrete in its fresh and hardened states were investigated. These are consistent as well and expand considerably the existing data basis on properties of concrete materials containing SAP. \ua9 2013 RILEM.Peer reviewed: YesNRC publication: Ye