MODIFICATION OF CALCINED CLAY AND ITS PHYSICAL PROPERTIES FOR USE AS A SUBSIDIARY MATERIAL FOR GROWING MEDIA

Calcined clay is a granular agglomerate of clay. It has a large surface area and myriad small pores, but also has a low easily available water (EAW) and water-buffering capacity (WBC). In this research, calcined clay was modified to enhance its low EAW and WBC and to allow it to substitute for subsidiary materials like perlite and vermiculite in growing media. To determine the proper size of the unit particles constituting the agglomerates for the matric potential of 1-10 kPa, several sizes of feldspar were agglomerated, and water suction tests were conducted. Based on the proper size, calcined clay was modified and made with kaolin through two steps. The first step consisted in consolidating kaolin by mixing it with water and drying it. It was then crushed and classified into the proper size. The second step consisted in agglomerating the kaolin spherically using a pan-type pelletizer. The fabrication of the modified calcined clay (MCC) was completed by heating it at 900 degrees C for 2 hrs. The granule of MCC was found to have bimodal pores: small pores with diameters of about 1 m, and pores larger than 10 m. Through the water suction tests of MCC and its mixture with Canadian sphagnum that were conducted, it was verified that MCC has higher EAW and WBC values compared to the typical calcined clay in growing media.