Technical news in construction materials

Clay Technology magazine
,
16 Aug 2016

A round-up of the latest technical news 

Sustainability cemented

A USA-based sustainable technology company has developed a new class of cement that cures with CO2 instead of water to form concrete, reducing the amount of water required, while sequestering CO2. Solidia Technologies claims its Solidia Concrete reduces carbon emissions by up to 70% compared with ordinary Portland cement production, and recycles 60–100% of the water used in the process. The cement is formed from a combination of calcium carbonate, wollastonite and silica and mixed with CO2, water and sand granules to form a concrete. 

A creeping feeling

The tendency of concrete to creep – progressively deforming under mechanical stress – can lead to crumbling structures, but now engineers at the University of California, Los Angeles (UCLA), USA, have identified a process that causes it. 

In a study published in The Journal of Chemical Physics, the researchers found that calcium-silicate-hydrates – the binding phase that holds cement paste together – tend to dissolve in areas under stress, and re-precipitate in low-stress sections. 

Lead researcher Gaurav Sant explained, ‘As a result of such dissolution-precipitation behaviour, a macroscopic, time-dependent creep deformation mainfests.’ A similar process is well known by geologists to occur in the earth’s crust, but this is the first time it has been observed in concrete. 

The team hopes to create a comprehensive description of concrete creep from the atomic to macroscopic scale, which would help in the development of mechanical models for predicting creep behaviour. 

Project aims for zero-waste ceramic tiles

A new ceramic paving material developed by researchers at the Institute of Ceramics Technology at Jaume I University, Spain, is made entirely from residues of tile production waste. 

The research is part of the European Commission-funded LIFECERAM project, involving the Spanish Ceramic Tile Manufacturers’ Association, and companies Chumillas and Tarongi, Keros Cerámica and Vernís, which aims to develop zero-waste ceramic tile manufacturing processes. 

Across the EU and Turkey, 1.8 billion m2 of ceramic tiles were produced in 2014, generating around 1.4 million tonnes of waste. While green tile scrap, frit waste and glaze sludge is already widely recycled, fired-tile scrap from red-firing normally isn’t, because of the high cost of milling the scrap and relatively low cost of red-firing clays. 

The researchers characterised the waste created in ceramic tile manufacture, determining the ceramic behaviour of waste processed with a series of mill and granulator variables, and defined properties such as shrinkage, porosity and colour. They then evaluated different combinations and dry milling and granulation systems to recycle the waste into a new product suitable for urban paving that would achieve as close to zero waste as possible. 

They found that a high-speed granulation system provided the optimal granule size distribution, most closely resembling the spray-dried powders used in the sector, and reduced the instance of larger granules, which are liable to generate defects in the tiles. 

A combination comprising 44.8% each of green and fired scrap, 7.5% glaze sludge, 2.5% polishing sludge and 0.25% kiln filter waste was found to be the most effective mixture. The softest wastes were milled in a hammer mill to under 300μm and the fired tile scrap to under 1mm, before high-speed granulation. 

While the material’s dry mechanic strength is lower than porcelain tile – 20kg/cm2, compared with 35kg/cm2 – at the 15mm thickness of flooring suitable for outdoor use (compared with 10mm for indoor), the researchers deemed it sufficient. 

Not only does the material make use of green and fired tile scrap, glaze and polishing sludge, and kiln filter dust – it does so in relative proportions to the amounts of each generated in manufacturing processes. The team has conducted successful pilot scale trials to validate its results. 

To find out more about the LIFECERAM project, visit lifeceram.eu