# Intensified Pozzolanic Reaction on Kaolinite Clay-Based Mortar  
[PERSON]  
1 Department of Architecture & Architectural Engineering, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul 08826, Korea; [EMAIL_ADDRESS] (Y.-H.K.); [EMAIL_ADDRESS] (S.-H.K.)  
[PERSON]  
1 Department of Architecture & Architectural Engineering, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul 08826, Korea; [EMAIL_ADDRESS] (Y.-H.K.); [EMAIL_ADDRESS] (S.-H.K.)  
[PERSON]  
1 Department of Architecture & Architectural Engineering, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul 08826, Korea; [EMAIL_ADDRESS] (Y.-H.K.); [EMAIL_ADDRESS] (S.-H.K.)  
[PERSON]  
2 Department of Civil and Environmental Engineering, National University of Singapore, 1 Engineering Drive 2, Singapore 117576, Singapore 2  
In addition to these industrial byproduct-based pozzolanic materials, there are natural pozzolans, such as volcanic ash [20], diatomaceous earth [21], and kaolinite mineral [22].  
As a sustainable building material, kaolinite clay (also known as hwangtoh clay in Korea) has been used for more than 1500 years in traditional houses in Korea, where there are enough reserves [23]. It consists primarily of kaolinite and quartz. Owing to its abundance and sustainable benefit, it has been studied by Korean researchers as a potential supplementary or main building material [23; 24]. The well-known advantages as a building material include high heat-storing capacity and its purifying, deodorizing, and antibiotic properties [25]. Moreover, when heating through Ondol (traditional floor heating system in Korea), the infrared radiation emission from the clay was confirmed to be beneficial to the human body [25]. With these advantages, it has been used as plastering, flooring, and finishing materials for buildings up to the present time [23; 26]. From a mix design perspective, the clay has been customarily mixed with sand and lime [27], as stated in Korean building standards [28]. However, the clay (the kaolinite mineral is the main reactive component in the clay) simply mixed with lime does not provide sufficient strength for construction applications. The main reason for the low compressive strength (<3 MPa) of kaolinite clay-based mortar (water-to-binder ratio of 0.5 to 0.6) is reported as the poor pozzolanic reaction between the kaolinite clay and lime [29]. This limits the application of this sustainable building material to mostly non-structural elements.  
To improve the mechanical strength of kaolinite clay, several studies were performed. The most well-known method to increase its reactivity is the heating of the clay up to 600 \({}^{\circ}\)C and above [4; 26]. OPC mixed with the heated kaolinite clay is also suggested [25; 30]. However, the heated clay with or without the OPC has a shortcoming of high energy consumption. The application of the geopolymer reaction using alkali activators is another interesting approach [23]. However, this also has disadvantages, such as significant workability loss because of rapid reaction, the hazard of handling an alkali solution, and high cost [31; 32]. In order to overcome these shortcomings, it is necessary to develop a new mixing formula for kaolinite clay-based mortar with improved material properties.  
In this study, a new mix proportion of the kaolinite clay-based mortar was developed. To increase its reactivity, an intensified pozzolanic reaction was intended by adding SF and hydrated lime together on the kaolinite clay. SF, known as microsilica, is a highly effective pozzolanic material due to its high silica content and extreme fineness [33; 34]. The addition of SF is expected to play a key role on the enhancement of material properties by providing the physical filling effect and the pozzolanic reaction with added hydrated lime. In this study, a series of experiments of compressive strength, heat of hydration, dimensional stability, and microstructural analysis was performed to evaluate the effects of the mineral admixtures on various material properties of kaolinite-based clay mortar.