Limestone Calcined Clay Cement as A Green Construction Material

Supplementary Cementitious Materials (SCMs) are promising components as substitutes for clinker components in cement and at the same time become a solution in reducing CO2 emissions and increasing sustainable development. The main objective of this study is to focus on production, techno-economic feasibility, and environmental impact, and cost-effectiveness of the limestone calcined clay cement (LC3). LC3 is a new type of cement-based on a blend of limestone and calcined clay. A combination of calcined clay with limestone allows higher levels of substitution down to clinker contents of around 50% with similar mechanical properties and improvement in some aspects of durability. The results showed that the feasibility of blending 50% of LC3 in cement. The hope is that these findings can help reduce carbon footprints in the construction industry. Article History: Received 02 Apr 2021 Revised 21 Aug 2021 Accepted 22 Aug 2021 Available online 23 Aug 2021 ____________________ Keyword: Cement, Clay, Green construction, Limestone, Supplementary cementitious materials (SCMs). ASEAN Journal of Science and Engineering Journal homepage: http://ejournal.upi.edu/index.php/AJSE/ ASEAN Journal of Science and Engineering 2(2) (2022) 157-166 © 2021 Universitas Pendidikan Indonesia Patil et al., Limestone Calcined Clay Cement as A Green Construction Material | 158 DOI: http://dx.doi.org/10. 17509/xxxx.xxxx pISSN 2776-6098 eISSN 2776-5938


INTRODUCTION
The limited supplies of conventional supplementary cementitious materials (SCMs) make it difficult to take this strategy further unless new types of SCMs become available. The only type of material available in the quantities needed to meet demand is clay containing kaolinite, which can be calcined to produce an effective SCM. Traditional Portland cement consists of 95% clinker. The production of it is energy-intensive and responsible for most of the CO2 within the cement. By reducing the clinker-content with so-called Supplementary Cementitious Materials (SCMs), large CO2 savings can be achieved (Rahla et al., 2019;Juenger et al., 2019).
Limestone calcined clay cement LC 3 is a new blend of two materials that have a synergetic effect. LC 3 can reduce CO2 emissions by up to 40%. It is made using limestone and low-grade clays which are available in abundant quantities. It is cost-effective and does not require expensive modifications to existing cement plants. LC 3 uses industrial waste materials which thereby increase resource efficiency and reduce the utilization of the scarce raw materials that are necessary for producing clinker (Avet et al., 2019). In other applications, LC 3 has the potential for applications used in prestressed and post-tensioned concrete members, used in masonry mortars and plastering, used in decorative and art structures, used in the manufacture of precast sewage pipes, used under harsh concrete conditions (Krishnan et al., 2018). Table 1 shows the chemical composition of LC 3 (Scrivener et al., 2018).
In this study, the objective of the LC 3 project is to research, testing and making LC 3 standard and mainstream general use cement in the global cement market. The main research activities focus on production, environmental sustainability, techno-economic feasibility, and cost-effectiveness of the LC 3 .

METHODS
The raw materials needed to produce mixed LC 3 -ordinary Portland cement (OPC) are clinker, limestone, kaolinite clay, and gypsum. To produce LC 3 , here are the steps: i) Clinker burnt at very high temperatures between 1400 and 1500°C, ii) Calcined clays are burnt at approximately 800°C, and iii) addition of limestone and gypsum to produce. In LC 3 production, gypsum content was varied (20, 35, 51, 80, and 95%).
Furthermore, the clinker used to produce LC 3 was also ground along with 5% gypsum to produce ordinary Portland cement (OPC) for comparison with the LC 3 blends. After the LC 3 and OPC were prepared, they were mixed with a mixture ratio of 60% LC 3 and 40% OPC. Figure  1 is an illustration of LC 3 production.

RESULTS AND DISCUSSION
LC 3 has been used in many different regions and different scales. Overall, more than 25 applications were already built with LC 3 . Figure 2 is the most prominent project is the model Jhansi, India. This house is made of 98% of LC 3 and it used 26.6 tons of industrial waste (192kg/sqm) and saved 15.5t of CO2 (114 kg/sqm). These CO2 savings are similar to the emissions of 10 passengers traveling by plane from Switzerland to South Africa.
There are also numerous other projects in India. For example, Figure 3 is the offices of the Swiss Agency for Development and Cooperation in the compound of the Swiss Embassy in Delhi that were built with LC 3 -prefab materials. Furthermore, Figure 4 is some roads, a check dam, and pavements that have been built.
In Latin America, several applications have been built. They are mainly in Cuba and also in other countries. Among those applications are an LC 3 house (       (20,35,51,80, and 95%) on the compressive strength of LC 3 cement was carried out. For the accomplishment of the study 6 mortors were produced. For the hardened state analysis, the compressive strengths were compared at the ages of 1, 3, 7, 28, and 91 days. From the result obtained it was possible to verify that gypsum content influences the compressive strength of the LC 3 cement. The highest mechanical strengths were obtained with the use of larger quantities of gypsum. Figure 8 shows the compressive strength of LC 3 .

Fineness
The effect of fineness of the different components in a blend containing 40% Portland cement and 60% of LC 3 . The higher fineness of both clinker and calcined clay can considerably improve compressive strength.

Durability
An extensive testing program is underway, including both laboratory and natural exposure studies. The results so far indicate: i) Good protection of reinforcement ii) Excellent resistance to chloride penetration iii) Good mitigation of ASR with reactive aggregates iv) Good performance in presence of sulfates v) Carbonation comparable to other blended cement The phases in LC 3 cement are the same as those present in blended cement currently widely used in practice. However, there is a high degree of refinement. The kinetics of pore refinement depends on the original kaolinite content of the calcined clay. In fact, at 28 days, all cement pastes made with calcined clays, even those with very low original kaolinite content; have a pore structure finer than pastes made with Portland cement.

Techno-Economic Feasibility of LC 3
LC 3 is very competitive in performance and economic terms. It shows very similar performance characteristics compared to conventional Portland cement and even outperforms traditional cement in some regards such as resistance to chloride and alkali-silica reaction (called ASR or "concrete cancer"). Apart from the laboratory testing at EPFL and the IITs, several applications have been constructed and they showed very positive results.
LC 3 is up to 25% cheaper in production due to the reduction of the energy-intensive clinker content with widely available and less energy-intensive materials. Investment costs are also low since already existing technologies can be used for the production of LC 3 . Moreover, this existing economic attractiveness can be further increased by governments through incentives such as tax reductions to accelerate the production of LC 3 .
LC 3 is a ternary cement that can achieve strengths similar to OPC even at clinker factors as low as 40% to 50%. The remaining cement is a blend of crushed limestone and calcined clay. LC 3 promises to support sustainable growth by reducing emissions, energy consumption, capital and production costs, and wastage of raw materials. LC 3 has been developed in an international collaboration between the University of Las Villas, Cuba, and Ecole Polytechnique Fédérale de Lausanne, Switzerland, which was funded by the Swiss government.
LC 3 takes advantage of the synergetic hydration of clinker, calcined clay, and crushed limestone to achieve the performance required from commercial cements, even at clinker factors as low as 0.40. The low-quality limestone and clay used in the LC 3 blend ensure that the cement can be produced at costs lower, without the risk of unsoundness. Since clays with low kaolinite contents, after calcination at relatively lower temperatures of 700°C to 800°C, can be used along with low calcite limestones with impurities such as quartz and dolomite, this cement can reduce wastage of raw materials and increase the life of mines. The lower processing required in the ingredients of LC3 ensures a lower capital investment required for the same incremental increase in production capacity.

Global Impact on LC 3
On a global level, it is estimated that the utilization of LC3 instead of regular cement can save up to 400 million tons of CO2 per year by 2050. This amount equals France's entire yearly carbon dioxide emissions. When looking at LC 3 in terms of frameworks such as the United Nations Sustainable Development Goals (SDGs), its potential to contribute to climate action efforts becomes clear. Among other contributions, LC 3 -Low Carbon Cement can be directly associated with 5 of the 17 Sustainable Development Goals. Figure 9 shows associated with 5 of the 17 Sustainable Development Goals.