Precast concrete slabs speed up housing delivery

Controlled conditions under Elematic SA’s state-of-the-art production facilities ensures a constantly high standard that is tested and fit for purpose

Precast concrete slabs speed up housing delivery

South Africa’s massive backlog in affordable housing is likely to see continued demand for precast hollow core concrete slabs from Elematic SA, given the high quality finish and the time that this technology saves in the construction process.

With rapid urbanisation and the increased premium on land in urban areas, multi-storey residential designs are now the norm,” says Elematic SA director Craig Webber. “This makes the use of pre-stressed concrete slabs an efficient and affordable solution, streamlining the pace of construction work while enhancing building quality and lifespan.”

The four-storey walk-up design, for instance, lends itself well to a repetitive construction methodology where precast comes into its own. Webber emphasises that the precast option eliminates the need for back-propping and allows other trades to start working under the slabs immediately, significantly accelerating the project schedule.

Moreover, the high quality finish on the soffit – or underside – of the slabs makes an additional false ceiling unnecessary, and eliminates this potential cost. The company’s precast staircases also lend themselves well to the fast track approach to many modern housing projects.

Using the traditional rib-and-block method of slab construction, contractors can wait about three weeks for concrete to cure fully, before props can be removed and work can commence.

By comparison, we install our precast slabs on one day and grout the next, allowing building to start on the third day without any further delay in the project timeline,” he says.

In operation since 2005, Elematic SA received ISO 9001 certification in 2009 and its products are approved by the South African Bureau of Standards

Manufacturing of these advanced precast products under controlled conditions in Elematic SA’s state-of-the-art production facilities on Gauteng’s East Rand ensures a constantly high standard that is tested and fit for purpose. As the largest producer of pre-stressed hollow core slabs in the Johannesburg area, the company’s two factories include 16 beds for a variety of slab sizes.

In operation since 2005, we received ISO 9001 certification in 2009 and our products are approved by the South African Bureau of Standards,” he says. “These quality standards underpin our products’ standing as among the most advanced in the industry, backed by the extensive knowledge and experience behind the Elematic brand.”

Helping the business sustain its quality standards is construction material leaders AfriSam, which provides a reliable supply of specialised cement – the Rapid Hard product in the 52.5R strength class – to Elematic SA’s factories near Benoni. AfriSam Rapid Hard cement is very fine, giving it a larger surface area to react with water, which increases the rate of hydration and gives it higher early strength.

This allows the manufactured concrete product to be released from the mould sooner, speeding up the production cycle and making factories as efficient as possible. It also provides consistent strength performance, so that the production processes can be timed with precision and without any danger of breakage due to weakness when removing products from moulds. The high early strength makes this cement brand ideal for pre-stressed members.

Elematic SA has been using AfriSam cement since 2007, relying on the product’s consistency and quality, and on AfriSam’s high level of customer service

The company has been using AfriSam cement since 2007, relying on the product’s consistency and quality, and on AfriSam’s high level of customer service. Like AfriSam, Elematic SA has its own ISO-accredited laboratories and testing equipment to ensure consistent quality; calibration of its test equipment is conducted regularly in line with SANAS standards.

Laboratory audits available for quarries

Laboratory audits available for quarries

Increasing requirements for certified quality aggregates has led the Aggregate and Sand Producers Association of Southern Africa (ASPASA) to introduce its own guidelines and auditing systems to ensure testing of aggregates and crushed granular materials is done in adherence to South African National Standards (SANS) 3001 AG and GR series test methods.

ASPASA member AfriSam’s Peninsula Quarry near Cape Town

This is indeed good news for the construction sector as this will further enhance the inherent quality of the full range of concrete, plasters and screeds.

In future, quarries which are members of ASPASA will have an option to participate in an annual audit designed to measure compliance of testing facilities including their apparatus calibration and personnel competence against an abridged ISO 17025 format, to assist in ensuring the correct classification of products. Over time, as their systems improve, they can opt to obtain accreditation through South African National Accreditation System (SANAS) for ISO/IEC 17025 – General requirements for the competence of testing and calibration laboratories.

According to Barry Pearce, chairman of ASPASA’s technical committee, the audits compliment the association’s well established environmental, as well as health and safety audit systems, which have contributed to the association’s recognition internationally as a leader in these fields.

Following procedures

Barry Pearce is the chairman of ASPASA’s technical committee and a Technical Assessor with SANAS. He manages his own CC, Learning Matters etc providing laboratory training and other materials related assistance to the civils and other related industry activities.

Now, the idea is to help ASPASA’s members to produce better graded products that are tested consistently to meet the specifications of their clients as well as national standards – where required. It entails the inspection of the laboratory including the testing apparatus and the verification of procedures.

The audits will be simple but thorough and will leave the quarry in no doubt as to what is required. With this in place producers can confidently supply their products without fear of material rejections in future, provided that the necessary procedures are followed.

It will also be tailored to the requirements of individual quarries which may range in size from a small family-owned quarry to large multi-national concerns producing aggregates and crushed granular material for multiple uses in different markets,” says Pearce.

Cost effective

He adds it is a fallacy that only large quarries can afford to have in-house laboratories. At the cost of a set of sieves, a flakiness gauge plate, some scales, a drying oven and containers, any quarry can setup the required tests to meet ISO 17025 requirements. Management systems can then be introduced at varying levels of detail depending on quarry’s requirements.

Pearce concludes that the construction and civils industry has long been working towards a more accurate system of materials procurement and the new ASPASA audits will go a long way to meeting and exceeding these industries requirements as well as improving the image of ASPASA and its members. The introduction of the technical audits is expected to reduce the rate of material rejection once delivered to site which is expected to easily offset the cost of compliance. He added the association would also look at participating in the National Laboratory Association – South Africa (NLA-SA) National Proficiency Testing Scheme (PTS) to assist in comparing results between the commercial facilities and ASPASA members to further reduce the disparities in the results and material rejections once the material has been delivered to site. Pienaar says that’s once the aggregate laboratories have been taken to a higher level, the experts with the help of Pearce could expand this focus area to the other members in the surface mines who are members of ASPASA, such as salt, silica and clay.