Mingshu Tang

A new accelerated method for determining the potential alkali-carbonate reactivity

Abstract Many kinds of carbonate aggregates with different chemical compositions, structure, and geological characteristics have systematically been investigated. This research deals with chemical components and mineral analysis, petrographic examination of the aggregates, the dynamics of alkali-carbonate reaction with different cements, alkali contents, and particle sizes. A new method for evaluating the potential alkali-carbonate reactivity has been proposed according to the results, in which the major test factors include 1.5% Na 2 O eq. of alkali content, 1 M NaOH solution, 0.3 water-to-cement ratio, 5–10 mm particle size, and 4 weeks of test period at 80 °C. The results using this new method has also been compared with that of the performance of concrete structures in China.

Effect of crushed air-cooled blast furnace slag on mechanical properties of concrete

Morphology characteristics of mix aggregates with crushed air-cooled blast furnace slag (SCR) and crushed limestone (LCR) with 5–20 mm and 20–40 mm gradation were represented by numerical parameters including angularity number (AN) and index of aggregate particle shape and texture (IAPST). The effect of mix aggregates containing SCR on compressive strength and splitting tensile strength of concrete was investigated. Fracture characteristics of concrete, interfacial structure between aggregates and matrix were analyzed. The experimental results show that porous and rough SCR increases contact area with matrix in concrete, concave holes and micro-pores on the surface of SCR are filled by mortar and hydrated cement paste, which may increase interlocking and mechanical bond between aggregate and matrix in concrete. SCR can be used to produce a high-strength concrete with better mechanical properties than corresponding concrete made with LCR. The increase of AN and IAPST of aggregate may enhance mechanical properties of concrete.

Potential Approach to Evaluating Soundness of Concrete Containing MgO-Based Expansive Agent

This paper will discuss how MgO-based expansive agent (MEA) has increasingly been used to compensate for the effects of thermal shrinkage of concrete in China. Long-term soundness of concrete containing MEA attracts much attention; however, the autoclave test, which is used to assess the soundness of cement caused by excessive intrinsic dead-burnt MgO, seems to be inapplicable to the reactive lightly burnt MEA due to its harsh and unreliable autoclaving condition. This study seeks a reasonable accelerated approach for ascertaining the relevant soundness of concrete made with this admixture. The effects of temperature on accelerating the hydration of MEA are investigated by curing cement pastes containing three types of MEA at 25, 40, 60, and 80°C (77, 104, 140, and 176°F) in water, respectively. Results of the expansion measurement of cement pastes and X-ray diffraction analysis on the hydration products of MEA indicate that the hydration of MEA is accelerated most effectively at 80°C (176°F), and it is fully reacted within a short period. This provides a new possible accelerated method. Soundness of concrete prisms containing MEA is investigated under the accelerated condition of 80°C (176°F) and the feasibility of this new approach is discussed.

Physical properties of crushed air-cooled blast furnace slag and numerical representation of its morphology characteristics

Physical properties and geometrical morphologies of crushed air-cooled blast furnace slag (SCR) and crushed limestone (LCR) were comparatively investigated. The shape, angularity, surface texture and internal pore structure of aggregate particles for different size and gradation were numerically represented by sphericity (ψ) and shape index (SI), angularity number (AN), index of aggregate particle shape and texture (IAPST), porosity and pore size, respectively. The results show that SCR is a porous and rough aggregate. Apparent density, void, water absorption and smashing index of SCR are obviously higher than those of LCR with the same gradation, respectively. However, bulk density of SCR is lower than that of LCR with the same gradation. SI, AN, IAPST and porosity of SCR are obviously higher than those of LCR with the same gradation, respectively. The smaller particle size of SCR, the larger of its AN, IAPST and porosity.

Investigation of Alkali-Silica Reaction Inhibited by New Lithium Compound

First, the effectiveness of Li 2 CO 3 against alkali-silica reaction (ASR) associated with a practical reactive aggregate was evaluated. The long-term effectiveness of Li 2 CO 3 in suppressing ASR was confirmed. Furthermore, the effective lithium dosage, as afunction of alkali content of cement-based materials, varies from 0.3 to 0.6 Li/(Na + K) molar ratio. Second, the influence of cement types on the effect of Li 2 CO 3 against ASR was also studied. It was found that larger expansion occurred with high-alkali cement than low-alkali cement either with or without Li 2 CO 3 , although the final alkali content was increased at the same level by adding KOH. This may be due to a relatively lower proportion of the total alkalis being incorporated in the cement hydrates, then, a higher proportion remains in the cement or concrete pore solution when the high-alkali cement is used versus the low-alkali cement. Third, the influence of Li 2 CO 3 on the strength and setting times of cement-based materials was performed. Results showed that mortar strength would decrease when Li 2 CO 3 was added, and the higher the Li 2 CO 3 dosage, the higher the strength reduction. Moreover both the initial and final setting time were shortened when Li 2 CO 3 was added, and the higher the Lil(Na + K) molar ratio of Li 2 CO 3 , the shorter the setting time. Finally, evidences of effectiveness of Li 2 CO 3 against alkali-silica reaction expansion was examined to confirm the hypothesis that because of having a smaller ionic radius and a higher surface charge density, the Li+ ions are more readily incorporated in the alkali-silica reaction product than Na+ or K+ ions, and the lithium-bearing ASR product is crystalline and nonexpansive.