Taijiro Sato

Cement and Concrete Nanoscience and Nanotechnology

Concrete science is a multidisciplinary area of research where nanotechnology potentially offers the opportunity to enhance the understanding of concrete behavior, to engineer its properties and to lower production and ecological cost of construction materials. Recent work at the National Research Council Canada in the area of concrete materials research has shown the potential of improving concrete properties by modifying the structure of cement hydrates, addition of nanoparticles and nanotubes and controlling the delivery of admixtures. This article will focus on a review of these innovative achievements.

Seeding Effect of Nano-CaCO3 on the Hydration of Tricalcium Silicate

A previous study indicated that the early hydration and strength development of ordinary portland cement (OPC) delayed by the presence of high volumes of supplementary cementitious materials were compensated for by the accelerating effect of nano-CaCO3. The mechanism responsible for the accelerating effect on the early hydration and strength development was, however, not fully understood. A study aimed at understanding the accelerating mechanism of the addition of nano-CaCO3 on the hydration of tricalcium silicate (C3S) is presented in this paper. A comparison with the addition of micro-CaCO3 was made. The hydration mechanism of C3S with the addition of micro- or nano-CaCO3 was studied by conduction calorimetry, thermogravimetric analysis, and scanning electron microscopy. The conduction calorimetry results indicated that the addition of nano-CaCO3 had an accelerating effect on the hydration of C3S as well as on the hydration of OPC. Furthermore, the induction period of C3S hydration was significantly shortened by the addition of nano-CaCO3. The results of the thermogravimetric analysis indicated that the amount of nano-CaCO3 decreased as the hydration of C3S took place; the decrease was greater with the hydration of OPC. The scanning electron microscopy revealed that the accelerating mechanism in the presence of micro-CaCO3 was considerably different from that of nano-CaCO3. Calcium silicate hydrate growth was observed around the nano-CaCO3 particles. The observation suggested that the seeding effect due to the addition of nano-CaCO3 was responsible for the accelerating effect on the hydration of C3S.

Reducing Set Retardation in High-Volume Fly Ash Mixtures with the Use of Limestone

High-volume fly ash (HVFA) concretes are attractive not only because they reduce cement content and the associated greenhouse gases, but also because they avoid landfilling excessive quantities of fly ash. These sustainability benefits are often tempered by practical constructability limitations that may exist for HVFA concretes: retardation and diminution of the early-age reaction, delay in setting (and finishing operations), and lower early-age strength. This paper explores the alleviation of these deficiencies in HVFA mixtures by the incorporation of fine limestone powders into ternary blends. Isothermal calorimetry and Vicat needle penetration measurements are employed to assess reaction rates and setting times, respectively. A systematic variation of the content and fineness of the limestone powder in mixtures containing either a Class C or a Class F fly ash indicates that setting times are linearly correlated with the surface area supplied by the limestone. Comparison of a limestone system to a system containing an inert titanium dioxide of similar particle size indicates that the acceleration and amplification effects of the limestone can be attributed to both physical (nucleation) and chemical (additional calcium ions) processes. The results indicate that ternary blends with 40% of the cement by volume replaced by 30% to 35% fly ash and 5% to 10% limestone at a constant water volume fraction can be achieved without significant delay in setting.

Increased Use of Fly Ash in Hydraulic Cement Concrete (HCC) for Pavement Layers and Transportation Structures

Fly ash is commonly used as a supplementary cementitious material (SCM) in the production of portland cement concrete. Concrete produced with high fly ash replacement levels is considered high volume fly ash (HVFA) concrete. HVFA concrete has many benefits, including reduced concrete production cost, reduced greenhouse gas emissions, and improved sustainability. Despite the advantages, there are several barriers that limit the use of HVFA concrete. One of the main limitations to the increased usage of HVFA concrete is the lack of contractor and transportation agency familiarity with the setting time and strength development of these concrete mixtures. For this research, a laboratory-testing program was developed to examine the effect of fly ash type, fly ash dosage, cement chemical composition, and environmental conditions on the hydration development, setting times, and compressive strength development of HVFA concrete. Results from semi-adiabatic calorimetry were used to develop a hydration model for HVFA concrete. Finally, the ConcreteWorks software program was used to predict the in-place performance of selected HVFA concrete mixtures when placed in various transportation structures. It is concluded that HVFA concrete may be produced to have comparable setting times and earlyage compressive strength development to conventional portland cement concrete when used for transportation infrastructure.