In this study was used three different clay types and sand from the local quarry in Latvia. Clay mass mixes were made by adding sand in each mix and remaining the same amount of clay proportion. Sand size particle amount was increased from 33% to 59%. Samples were extruded with laboratory extruded as full brick samples. After formation samples were dried at 105
C and fired at 1000
C for 1 h. Water absorption, shrinkage, density, compressive strength were measured after the firing process. The crack amount was determinate by the digital camera after drying process and after firing process. Fired sample cracks start/end points were analysed with SEM-EDX.

Introduction

In many quarries clay granulometry variates in the wide range from very plastic clay with high clay size particle amount till sandy clay with high silt and sand-size particle amount. It is very important to control and adjust it with additives for production, to minimize varieties in granulometric because that can affect product quality and properties after firing [1]. Quality control must be done by analyzing granulometric data, clay mass moisture content during forming, drying shrinkage, firing shrinkage, water absorption, and other properties. In production, a quality control process is important that ensures that a good product reaches the customer and meets his needs, like thermal conductivity, strength, home environment and visual aspect [2,3]. Quality of the brick must be controlled through all manufacturing process, starting with material testing, formed green brick, dried brick and fired brick. One of the quality tests is visual inspection – brick cracking. First cracks can be visually observed after drying. Drying rate must be set right to not cause too fast temperature increase. In the manufacturing process drying usually happens in the drying tunnel. Brick temperature is increased 30–۸۰
C to evaporate free water from bricks. A drying tunnel is split into 3 parts. In the first part of the tunnel, a brick air temperature is about 50
C and relative humidity is around 80%. In the second part of the tunnel, drying air temperature is kept constant and relative humidity is starting to fall due to a brick moisture decrease and tunnel fans that suck out wet air from the drying zone. In the third part is a temperature of brick is around 80
C and moisture content is around 3% [4].