Formation Of Carboaluminate Research Articles

Impact of Limestone–Metakaolin Ratio on the Performance and Hydration of Ternary Blended Cement

Once sulfates become limited, the interaction of limestone with metakaolin (MK) is initiated, resulting in the formation of carboaluminates in a blended cement system. In this study, two different types of MKs (sourced from coal mining residue and soft clay) were adopted to examine limestone–MK ratios of 1:8, 1:4, 1:2, 1:1, and 2:1, by fixing the cement and MK content at 55% and 15%, respectively. The optimal limestone–MK ratio of 1:4 was found (equal to limestone content of 3.8%) to achieve the highest compressive strength of 60 MPa due to the formation of more carboaluminate content in both MK blended cement systems. This finding was corroborated with the thermodynamic modeling that the highest hydrates volume was achieved at the optimal limestone–MK ratio of 1:4. An overdosage of limestone reduces its reaction degree, reflecting the fact that excessive limestone content could only acts as filler in the system.

Limestone calcined clay cement: mechanical properties, crystallography, and microstructure development

Limestone calcined clay cement (LC3) holds promise as a new type of sustainable cement-based material, but the mechanisms underpinning its engineering performance are still poorly understood. Here, a metal intrusion-enhanced imaging approach was employed to quantitatively analyze and link the pore structure development of LC3 to its hydration process, i.e. solid-phase development, and mechanical performance. We found that the early age microstructural development in LC3 is inhomogeneous, with the perimeter of limestone particles displaying higher porosity relative to that surrounding calcined clay and clinker. At later ages, the formation of carboaluminates and calcium-aluminate-silicate-hydrates homogenized the overall microstructure of LC3, thereby delivering improved mechanical performance. Overall, our analysis suggested a more efficient particle packing in LC3 mixes, which decreases the volume/connectivity of micro-pores and can account for LC3’s notable flexural strength. These findings can assist the development of improved LC3 binder formulations alongside other ternary binders with possibly higher limestone additions.

Research Progress on the Hydration of Portland Cement with Calcined Clay and Limestone

The use of calcined clay and limestone as supplementary cementitious materials, can have a certain influence on the hydration of Portland cement. This paper reviewed the influence of limestone and calcined clay and the mixture of limestone and calcined clay on the hydration of cement. Both limestone and calcined clay accelerate the hydration reaction in the early hydration age and enhance the properties of cement. Limestone reacts with C3A to form carboaluminate, which indirectly stabilized the presence of ettringite, while calcined clay consumed portlandite to form C-(A)-S-H gel, additional hydration products promote the densification of pore structure and increase the mechanical properties. The synergistic effect of calcined clay and limestone stabilize the existence of ettringite and stimulate the further formation of carboaluminate, as well as the C-(A)-S-H gel, contributed to a dense microstructure.

Recycling Blast Furnace Ferronickel Slag as a Replacement for Paste in Mortar: Formation of Carboaluminate, Reduction of White Portland Cement, and Increase in Strength.

Blast furnace ferronickel slag (BFFS) is generated in the production of ferronickel alloys and is used as cement replacement in concrete or mortar. The effectivity in reducing cement consumption and improving performance are limited. By referring to the paste replacement method, this work used BFFS to replace an equal volume of the white Portland cement paste to obtain greater performance enhancement. BFFS was used with five levels of replacement (0%, 5%, 10%, 15%, 20%) and four water-to-cement ratios (0.40, 0.45, 0.50, 0.55) were designed. Fluidity, mechanical strength, hydration products, and pore structure of every mixture were measured. The results showed that the workability of the mortars decreased due to the reduced volume of water, but the 28-day compressive strength of the mortars increased, and the cement content of the mortars was also reduced by 33 wt %. The X-ray diffraction (XRD) patterns revealed that there existed a carboaluminate phase, and the presence of the ettringite was stabilized, indicating that the accumulating amount of the hydration products of the mortar increased. Furthermore, the BFFS could consume the portlandite and free water to form a higher amount of chemically bound water due to its pozzolanic activity. A high degree of hydration and a large volume of the hydration products refined the porosity of the hardened mortars, which explained the enhancement of the strength of the mortars. Compared to the cement replacement method, the paste replacement method was more effective in preparing eco-friendly mortar or concrete by recycling BFFS for reducing the cement content of the mortar while improving its strength.

Influence of cement replacement by limestone calcined clay pozzolan on the engineering properties of mortar and concrete

This study investigates the effect of a new type of blended pozzolan on the hydration, mechanical and durability performance of cement. A blend of limestone calcined clay pozzolan (LCCP) was produced by grinding calcined clay and limestone in a ratio of 2 : 1 with 2% gypsum. Blends with cement replacement level of 0, 10, 15, 20, 30 and 50% using LCCP were cast. The effect of LCCP on the hydration of cement was investigated using isothermal calorimetry and X-ray diffraction. Mortar and concrete samples were cast to study the influence of LCCP on mechanical and transport properties. The addition of LCCP was found to have a beneficial effect on the early age hydration of cement. The induction period and initial setting time of cement paste were found to reduce on increased cement replacement level. Higher or similar compressive strength was observed for all the LCCP blends as compared to ordinary Portland cement. The pozzolanic reaction of calcined clay and formation of carboaluminates on the reaction of calcium carbonate with alumina helps to develop a refined pore structure that aids in reducing transport properties of concrete such as porosity, rate of water absorption and permeability.