Review abstract on durability of new and reused fired clay bricks

One of construction materials' most essential sustainability parameters is durability, enabling to prolong the value of already used resources. Due to already existing experience with reuse of fired clay bricks, this material is seen as one of the frontrunners for the reuse of construction materials. However, in contrast to earlier, today reuse of existing fired clay bricks in new constructions is met with a demand to declare and document materials, to avoid reduced and insufficient durability of some reused fired clay bricks (see Figure 1).

To predict the future, accelerated aging may be studied with different approaches reflecting real-life deterioration (salt weathering, freezethaw, wetting-drying, chemical reactions, biological colonization, thermal cycles, heating, exposure to ultraviolet radiation, exposure to weathering agents in the outdoors), where salt weathering is the most used [1]. Several accelerated aging tests with salts were used for research in the past, RILEM MS-A.2 and EN 12370 but showed a lack of coherence between damages observed in praxis and those observed after aging tests in the laboratory. Also, today durability of fired clay bricks is still experienced-based. Recently a new procedure has been developed within the RILEM TC 271-ASC, with the aim to reflect more realistic aging with the least circumstantial test procedure. The hope is that this procedure will find its way also into tests of newly fired clay bricks. The existing practice with experience-based durability classes of fired clay bricks based on decades of feedback from practice, make it possible to create a link to aging tests. Based on this, a systematic study on used durability classes in Denmark (MX1, MX3.2, MX3.2+4) along with the results from the variety seen on reused bricks has been made. Further relevant durability material properties (density, Water Absorption Coefficient, and 24-hour capillary suction) have been identified based on insights from theoretical salt damage mechanisms and linked to the experience-based durability classes and found proven after aging tests with the new RILEM TC 271-ASC test procedure [2]. In addition, material properties and salt weathering have been linked to raw material preparation and firing conditions [3]. These steps are necessary to transfer durability assessment from experience-based into knowledge-based durability documentation.

The next step, and ongoing, is to develop still less time-consuming methods for durability prediction without significantly compromising the results, contributing to a more approachable quality control method of reused fired clay bricks. Presently a measuring technique based on electromigration, and the setup described in [4] is examined as a potential method for faster durability determination. In parallel freeze-thaw testing is to be carried out to examine consistency and/or supplementing outcome of salt and frost durability testing, since the pore size distribution of the fired clay brick will determine its susceptibility to salt (<0.050 μm) [5] and frost (>0.8μm) [6] respectively.