Estudo das matérias-primas e tijolos cerâmicos furados produzidos no Estado da Paraíba.

Abstract

The present work is a contribution to the study of raw materiais and red heavy clay products to be used in buildings, specially as ceramic bricks produced in the state of Paraíba. A study was conducted to characterize the raw materiais employed by potteries and small brick factories as well as the end products - bricks -usually supplied to the market, according to ABNT rules. For many years, recent quaternary clays have been largely used to produce red ceramic products, such as bricks and roofing tiles. These products are not only extremely important for the building industry but also they are the most largely produced in the state of Paraíba. Most pottery and brick factories do not have a quality control program to guarantee their products and there are hardly any systematic studies with this kind of raw material which renders it difficult to improve these products and, consequently, to introduce new industries and factories with appropriate standards. The present research was conducted on rectangular profile specimens (6,0 x 2,0 x 0,5cm3) which were compression moulded (20 MPa) from semi-dried mass. This model allowed us to measure the specimens physical-mechanical or ceramic properties after drying at 110°C and after curing at 900°C, 1000°C and 1100°C. The ceramic properties in the green state and after curing were compared with the limiting-values recommended by Souza Santos as well by Barzaghi and Salge. The results obtained for the clays analysed indicated that, according to Souza Santos' specifications, only 16% of the samples investigated can be used as red ceramics and, according to Barzhaghi and Salge's specifications, 72% of the clays investigated can be used in the production of solid bricks, 44% for cored bricks and 32% can be used to produce roofing tiles if a curing temperature of 900°C is considered. This temperature was chosen as the closest curing temperature actually employed in red ceramic products for the building industry. With respect to the bricks, we concluded that none of the 25 samples investigated comply with ABNT specifications. The results obtained clearly show. that there is no effective contrai on the praduction step of these bricks. The large variation obtained on compression strength and water absorption of each sample indicate praduction problems, mostly with respect to raw material homogeneity since there is no contrai on clay particle size, disposition of the blocks in the oven and curing temperature. Most of the blocks tested showed a characteristic behaviour associated with badly-cured bricks. They noncompliance to technical specifications makes it difficult to rationalize the building process as well as to execute it which leads to significant losses to the market place.