Limestone Calcined Clay Cement Research Articles

New ternary blend limestone calcined clay cement for solidification/stabilization of zinc contaminated soil

This study evaluates the potential use of a new limestone calcined clay cement (LC3) for stabilization/solidification of zinc contaminated soil. LC3 is a new ternary blend manufactured by the replacement of 50% cement clinker by locally available two supplementary cementitious materials (SCMs) - limestone and calcined clay. The incorporation of LC3 is evaluated on the soil spiked with 0.5% and 1% of Zinc (Zn) at curing times of 3, 7, 14, 28 and 56 days. pH, strength and leachability properties of the solidified/stabilised soil are measured for both mechanical and environmental conditions. Additionally, sequential extraction procedure (SEP), X-ray diffraction (XRD) analysis and scanning electron microscope (SEM) analysis are performed to elucidate the mechanisms of Zn immobilization in the soil. The results show that the leachable Zn concentrations in the stabilised soil are well below the corresponding hazardous waste management regulatory limit after the curing time of 14 days. The soil pH and unconfined compressive strength of the stabilised soil increase with curing time. The SEP results confirm that LC3 considerably reduces the acid soluble fraction (F1) and increase the residual fraction (F4). The XRD and SEM results indicate that formation of Tri-calcium Silicate 3CaO·SiO2, Portlandite Ca(OH)2, Ettringite Ca6Al2(SO4)3(OH)12.26 H2O and Wulfingite Zn(OH)2 are the primary mechanisms for the immobilization of Zn in the LC3 stabilised soil.

Service life and life cycle assessment of reinforced concrete systems with limestone calcined clay cement (LC3)

This paper presents data on the chloride diffusion coefficient (Dcl), ageing coefficient (m) and chloride threshold (Clth) related to seven concrete mixes (four M35 and three M50) with OPC, OPC + PFA (pulverised fuel ash) and limestone-calcined clay cement (LC3). Using these, the service lives of a typical bridge pier and girder with the PFA and LC3 concrete were found to be much higher than those with OPC concrete of similar strength. From life-cycle assessment, the CO2 footprint of PFA and LC3 concrete were found to be significantly lower than those of OPC concrete of similar strength. Further, the CO2 emissions per unit of concrete per year of estimated service life, as a combined indicator of service life and carbon footprint, are similar for concrete with PFA and LC3, which are much lower than that with OPC.

Impacting factors and properties of limestone calcined clay cements (LC3)

This paper details the main factors influencing the performance of limestone calcined clay cements (LC3). The kaolinite content plays a major role in the rheological properties as well as strength development. Even in the presence of secondary phases, kaolinite can be accurately quantified by thermogravimetric analysis. The performance of LC3 is slightly influenced by the calcination process of clay, but it can be optimized by using the correct calcination temperature and applying a specific mix design with adjusted sulfate and alkali content. The hydration reactions of LC3 are fully characterized. They vary slightly from plain cement. There is no significant change in terms of phase assemblage. The main properties of LC3 are also described. LC3 blends show a lower creep compliance and a delay in shrinkage strains compared with plain cement. Concerning durability, LC3 blends show outstanding performance with respect to resisting chloride ingress and expansion from the alkali–silica reaction.

Investigation of C-A-S-H composition, morphology and density in Limestone Calcined Clay Cement (LC3)

In this study, the C-A-S-H composition, morphology and density are characterized for Limestone Calcined Clay Cement (LC3-50) blends containing clays with various kaolinite contents. Significant incorporation of aluminium is observed for LC3-50 blends compared with reference Portland cement (PC), and this incorporation increases with the kaolinite content of the calcined clay. No change of C-A-S-H morphology was observed by Transmission Electron Microscopy (TEM) between reference PC and LC3-50 blends, with a “fibrillar” morphology for all samples. The determination of the density of C-A-S-H measured by 1H NMR also shows very similar results with a bulk density close to 2.0 g·cm−3 and a solid density of around 2.8 g·cm−3 for all systems.

Performance of Limestone Calcined Clay Cement (LC3) with various kaolinite contents with respect to chloride transport

The durability of mortar and paste mixtures with respect to chloride ion ingress was investigated for binary blends of Portland Cement Calcined Clay, and ternary systems of Limestone Calcined Clay Cement (LC3). Five clays from various sources with different kaolinite content (17–95%) were studied. The main factor controlling the diffusivity of LC3 systems was found to be the kaolinite content of the clay. Resistance to chloride ingress increased to intermediate levels of kaolinite content and then stabilized. An intermediate kaolinite content of around 50% resulted in two orders of magnitude reduction in diffusivity compared to PC, indicating that the use of high grade (expensive) clays is not necessary to obtain good durability. The chloride binding capacity and distribution of bound chloride between Friedel’s salt and C–A–S–H were quantified for the different systems at fixed water to binder ratio of 0.5. The chloride binding capacity appeared to be a minor factor compared to the porosity refinement in the improved durability of LC3 systems.

Changes in microstructure characteristics of cement paste on carbonation

This study investigates the influence of carbonation on the microstructure of cement paste cast with Ordinary Portland Cement (OPC), fly ash based Portland Pozzolana Cement (PPC) and Limestone Calcined Clay Cement (LC3) using X-ray diffraction (XRD), thermal analysis (TGA), scanning electron microscope (SEM) and mercury intrusion porosimeter (MIP). A comparison is made between samples exposed to 3% carbon dioxide concentration and those exposed to natural CO2 concentrations. It is observed that the products formed on carbonation are similar in both the exposure conditions. Distinct rims corresponding to decalcified C-S-H are observed around clinker grains in the carbonated samples. Coarsening of pore structure is observed on carbonation in all the cements and an increase in the total porosity is observed in blended cements. Thermodynamic modeling indicates irrespective of the type of cement the total solid volume is reduced on complete carbonation. The volume change occurring on carbonation obtained from experimental results and thermodynamic modeling are compared.

Mechanical properties and durability performance of concretes with Limestone Calcined Clay Cement (LC3)

The adoption of any binder system for structural concrete depends on the performance characteristics desired for addressing the long-term deformation and durability concerns. The major properties influencing the performance includes the shrinkage characteristics governing the long-term deformation, and durability characteristics related to various transport mechanisms, governing the performance in different service conditions. This paper describes the potential of Limestone Calcined Clay Cement (LC3) for use in structural concrete in comparison with Ordinary Portland Cement (OPC) and fly ash based blended cement (FA30). Three types of concrete mixtures were designed for the study, two based on achieving an equivalent strength grade (M30 and M50 concrete grade) with each binder, and the third with equal binder content and w/b ratio. Mechanical properties such as compressive strength and elastic modulus, and autogenous and drying shrinkage, along with various durability parameters of the different concretes were assessed. Oxygen permeability, rapid chloride penetration, chloride migration, resistivity development and water sorptivity were the various parameters considered for evaluation of durability performance. The results indicate the superiority of LC3 binder over other binders in producing durable concrete, especially in a chloride laden environment. The major reason for the better performance was attributed to the more compact and dense microstructure of the system with the LC3 binder against OPC and FA30. The drying shrinkage performance was seen to be similar for concrete with all three binders.

Investigation of the calcined kaolinite content on the hydration of Limestone Calcined Clay Cement (LC3)

This study presents the influence of the calcined kaolinite content of calcined clays on the hydration of Limestone Calcined Clay Cements containing 50% of clinker (LC3-50). Above a calcined kaolinite content of 65% in calcined clay, further reaction of clinker is inhibited from 3 days onwards. Detail investigation indicates that this slowing down of clinker hydration is related to a significant refinement of pore connectivity. A limiting critical pore entry radius of 3–5 nm is reached, from which the porosity does not get further refined. The higher the calcined kaolinite content, the faster this refinement limit is reached. The formation of carboaluminate hydrates is also limited after reaching this refinement limit. As a consequence, the on-going reaction of metakaolin impacts C-A-S-H, mainly affecting gel porosity, which is not well characterized by MIP.

Determination of the amount of reacted metakaolin in calcined clay blends

This paper presents a comparative study of three methods to determine the amount of reacted metakaolin in calcined clay blends: mass balance, thermodynamic modelling, and the Partial or not Known Crystalline Structure method (PONKCS) based on Rietveld analysis of X-ray diffraction. The methods are applied to Limestone calcined clay cements (LC3-50) in this study. Mass balance and thermodynamic modelling results show good agreement, especially at early age. PONKCS method shows globally comparable results, even if it has higher variability. The precision of PONKCS becomes poor for blends with <60% of metakaolin in calcined clay.

Assessment of pore structure evolution in the limestone calcined clay cementitious system and its implications for performance

Use of limestone and calcined clay together for clinker substitution makes an effective low clinker cement blend, which shows promising mechanical properties at early ages. The performance of these cementitious systems strongly depends on the pore structure, which is a dominant factor governing the durability characteristics because of its direct influence on the transport properties. The experimental study described in this paper on three different binder systems including Ordinary Portland Cement, Portland Pozzolana Cement - with 30% Type F Fly Ash (designated FA30) - and Limestone Calcined Clay Cement (LC3) pastes shows that the LC3 system attains greater refinement of the pore structure as early as 3 days, as seen from mercury intrusion porosimetry. Electrical measurements also reveal lower conductivity in the system, which suggests better resistance to ionic transport in the binder phase. The results of hydrate phase assemblage studied by X-ray diffraction also indicate that greater amount of hydrates contribute in a major way to the reduction in the (water-filled) porosity in all the systems. This change occurs at varying rates for the different systems due to the difference in hydration characteristics. The estimated permeability suggests that the LC3 binder system attains much lower permeability compared to the ordinary Portland cement and FA30. A comparison of the formation factor shows distinct differences in the microstructural development and suggests a more durable binder with LC3 cementitious system.

Assessing the environmental and economic potential of Limestone Calcined Clay Cement in Cuba

Cement is the most produced material around the world. Developing countries face a growth of population involving an increasing need of infrastructures. Due to this situation, the cement industry needs to find the best comprise between increasing the cement production and without increasing the negative environmental impact. A promising solution has been found in the use of supplementary cementitious materials (SCM), these materials are used to replace clinker in cement because of their pozzolanic reactivity. In this paper, a method was developed to assess the details of the economic and environmental potential of the specific Limestone Calcined Clays Cement LC3 technology in the Cuban context. A comparison with traditional Portland cement and the current commercial blended cement with zeolite (PPC) sold in Cuba was made. The results provide evidenced based data for the development of a strategy to adopt the LC3 technology by the Cuban market. This assessment method can then be easily extended to markets in other developing countries.