WALLS & ROOFS takes a look at new research projects, issues to address and new developments regarding bricks and concrete masonry.

Bricks and concrete blocks have formed the basis of South African buildings for many years and are seen in abundance across the country. Durable and uniquely suited to the local climate, the materials have been our go-to solution for any type of construction through both tough times and prosperous stints, and prevailing against evolving architectural trends and regulatory changes in the construction industry.

The past few years have been especially trying for the building industry as a whole, but has affected the manufacturing of bricks and concrete blocks in particular.

“An analysis of private residential and non-residential building plans passed and buildings completed, shows an industry that is tentatively recovering,” remarks Julian de la Hunt, president of the Clay Brick Association of South Africa (CBA). “The total investment in building and construction for 2014 remained flat and in the rural areas particularly, it has been a difficult year.”

Clay bricks: A cost-effective option
Despite the harsh financial climate, clay brick still remains one of the most economical walling materials available. The long lifespan and structural integrity of clay brick structures, according to the CBA, is in part due to their high load-bearing capacity, high dimensional stability and compressive strength. Clay brick is a passive material that is completely incombustible, and as a result the material has a maximum fire rating. It also does not release volatile organic compounds (VOCs) or toxic fumes.

“Brick masonry does not promote mould growth, even if wetted, it contains no pollutants or allergens and is resistant to ants, borers and termites,” adds Jonathan Prior, executive director of the CBA.

Kiln emissions lower than anticipated
A major air quality initiative for the CBA has been research into clamp kiln emissions to establish an accurate benchmark for the discharge of sulphur dioxide, nitric oxide, particulates, smoke and dust.

“By 2017, the Energy-Efficient Clay Brick (EECB) Project anticipates an overall annual reduction in greenhouse gas emissions from the South African clay brick sector of 320 000 tons of CO₂ per year,” says CBA technical director, Nico Mienie. “This represents a reduction of 10%.”

The National Environmental Management Act (2004) has identified clamp kilns as an activity that results in atmospheric emissions. As it is difficult to accurately measure emissions from open-air kilns in brickyards with different environmental and climatic factors, the Environmental Engineering Group at the University of Pretoria (UP) constructed a model kiln which allowed them to accurately measure only emissions generated by the kiln.

After three years’ research and four successful firings over periods of 10 to 14 days, it was found that the particulate matter emissions are about 20% lower and nitrogen oxide emissions moderately lower than the standard factor stated in best-practice literature. In addition, it was proven that sulphur dioxide emissions are in direct proportion to the fuel used, and sulphur can be removed from fuels before burning, although it will raise costs significantly.

This means that surrounding farms and other activities surrounding the kilns might contribute more emissions than previously thought, and improving dust control for quarries, dirt roads and distribution hubs therefore may have a bigger impact on reducing emissions than changes to the kiln itself.

Bricks benefit people
Another CBA project nearing completion is the Socio-Economic Lifecycle Assessment, which studies the economic impact of clay brick manufacturing on communities across South Africa. In terms of job creation, it is estimated that 32 000 people are directly employed in brickmaking in South Africa through formal and informal brick makers, while about 220 000 workers are employed across the building industry, including brick layers, plasterers and resellers.  

“Initial results indicate that more than one million people benefit from clay brick manufacturing,” says CBA vice-president and marketing director, Musa Shangase. “Due to low capital requirements, and the wide use of masonry materials in both urban and rural areas, more entrepreneurs are involved in brick and block laying than any of the alternative wall construction types.”

New: Lightweight thermal blocks
An Irish company has recently developed and launched a lightweight concrete block with an excellent thermal conductivity value of 0,33W/mk for use with traditional masonry wall construction.

Manufactured using a special mix which includes lightweight aggregates, one such block has an average weight of just 11,5kg compared to the standard 20kg concrete block. But despite being lightweight, it is robust and durable with a minimum compressive strength of 5N/mm2. Compliant U-values are achieved without having to provide a cavity in excess of 150mm.

Development: Repairing cracks with bacteria
Having spent several years doing research on self-healing concrete, which sees concrete materials repairing their own cracks with the help of bacteria, a team from the Delft University of Technology has for the first time applied the technology at a lifeguard station in the Netherlands.

This biological solution involves bacillus bacteria, which are hardy and long-living, plus its food source, calcium lactate, being packed into tiny capsules that dissolve when water enters the concrete cracks. Once the bacteria are released and consume the calcium lactate, a chemical reaction causes limestone to form, which fills the crack.

Innovation: Mushroom brick tower
Last year, an organic brick tower was constructed using mushroom brick technology. The self-assembling bricks consist of agricultural waste and mycelium and can be grown to fit a brick-shaped mould in only five days. This innovative building material was developed by Ecovative, and is completely organic and therefore 100% biodegradable.

Advancement: Nanomaterials
A research paper entitled “The influence of cellulose nanocrystals (CNCs) additions on the performance of cement paste” shows that CNCs can increase the tensile strength of concrete by 30%, signifying a potential additive which can improve this universal building material.

Normally, not all of the cement particles are hydrated after being mixed, but nanocrystals increase the hydration of the concrete mixture, allowing more of it to cure, thereby strengthening the structure of the concrete while requiring less cement.

These nanocrystals are extracted from cellulose micro-fibrils in plants and trees, but can be derived from by-products in the paper, bioenergy, agriculture and pulp industries, and are therefore a renewable material that is abundantly available.

Having been around the block a couple of times, both the brick and concrete masonry industries worldwide are keen to evolve and keep up with the times. Becoming more sustainable and stronger in terms of manufacturing processes and composition, these materials are sure to be around for many more years.

Full thanks and acknowledgement are given to the Clay Brick Association of South Africa, inhabitat.com, www.roadstone.ie and www.archdaily.com for the information given to write this article.

Highlights:
•    Clamp kiln emissions are lower than previously thought.
•    A total of 32 000 people are directly employed in brickmaking in South Africa.
•    An estimated 220 000 workers are employed in brick construction across the building industry.
•    A new lightweight, thermal block has been developed in Ireland.
•    Self-healing concrete using bacillus bacteria has been applied for the first time.
•    Innovative, organic bricks are grown from agricultural waste and mycelium in five days.
•    Naturally available cellulose nanocrystals can increase the tensile strength of concrete by 30%.