Africa’s largest manufacturer of concrete brick, block and paving machinery and concrete equipment supplier, Pan Mixers South Africa (PMSA), won the contract in mid-2014 to build and commission the Van Dyk Stene plant, in Vredenburg, in the Western Cape. PMSA was contracted to supply all equipment for the plant, with the project taking about nine months from design to completion.
PMSA was able to offer product manufacturer Van Dyk Stene and plant owner Andre Van Dyk a comprehensive automated solution which includes batching – mixing and weighing the material – transporting the material to the block-making machine, supplying the actual RE1400 block-making machine and automated wet and dry side product handling.
As this is an automated plant, PMSA was also able to supply the stacker and destacker, as well as the leading technology used in the curing process, provided by Germany-based concrete curing solutions provider Kraft Curing. The Van Dyk Stene plant started operations in March and is now able to operate 24/7, if required.
The total plant investment was about R20-million, which was funded by Van Dyk Stene.
This is the first plant at which PMSA has implemented the Kraft Curing technology in Africa. PMSA is the official distributor of Kraft Curing’s solutions in Southern Africa. The Van Dyk Stene plant is also one of the first plants in Africa to use a full curing system and the only plant in South Africa that uses a full Kraft Curing system.
“Many of our clients use a racking system, but not all of them have a full insulation and circulation system to control the temperature and the humidity of the curing chamber,” says PMSA marketing and sales manager Quintin Booysen.
He tells Engineering News that the Kraft Curing technology used in the plant is part of the comprehensive concrete solution that PMSA was contracted to supply to Van Dyk Stene, adding that PMSA clients’ demand for this technology has been on the increase.
Booysen notes that, like any manu- facturer of precast products, the ultimate goal is to identify where costs can be reduced.
One sector in which costs will be reduced at the Van Dyk Stene plant is labour, owing to the automated technology used in the plant. Booysen explains that the more labour-intensive the plant is, the more expensive the bricks will be.
Booysen further notes that, with most of its clients, the cement cost contributes to 30% or more of the actual cost of a brick . Therefore, if costs can be saved on cement without compromising quality, the product can be made cheaper.
“It is not easy to save costs on cement. Previously, brick manufacturers would have had to optimise their production facilities with the least amount of cement possible, which would have to be stabilised using admixtures and certain techniques,” says Booysen.
However, he explains that using the curing system results in the curing chamber being insulated with temperature and humidity control, which subsequently keeps the heat inside and humidity and temperature fully controllable. If the heat and humidity can be increased during the curing process, the cement will hydrate better, subsequently resulting in a better-quality end-product with a lower cement content.
“The curing system allows for a very high level of humidity inside the chamber, which enables the concrete to cure and set better. It also makes the hydration process more effective, so manufacturers are getting more efficient use of their cement, which ultimately enables them to lower the cement percentage, but keep the same strength,” says Booysen.
Racking vs Curing Systems
Booysen says people tend to think that a racking system is the same as a curing system. He explains, however, that they are completely different. A racking system allows for cement products to be racked which means the products are stacked above each other on racks without any type of housing or air recirculation system, whereas a closed insulated and ventilated curing system controls the humidity, air speed and temperature inside the curing chamber and, if necessary, it can add extra steam if the vapour generator is fitted and required.
He highlights that some of the benefits of Kraft Curing’s system include temperature consistency; relative humidity consistency maintained between 90% and 95%; improved operational efficiency; and high early concrete strengths, uniform colour, and a denser product surface. The curing system can also increase cement use efficiency, reduce cement cost and reduce efflorescence in products, which refers to a crystaline deposit on surfaces of masonry, stucco or concrete, which is whitish in appearance.
The curing system also allows for air circulation that maintains temperature consistency throughout the top and the bottom of the chamber and, together with increased humidity, results in even strength throughout the product. High early strengths in the product means that it can be tested and delivered faster, thereby reducing stockholding.
Booysen notes that the humidity and temperatures achieved at the plant are not generated for external power sources, and that the insulation, and the even distribution and circulation of heat in the Kraft curing chamber, produce free energy from the heat of hydration process in the concrete, so that, technically, the bricks are greener, as less cement is used and the embodied energy of the cement is used better as part of the curing process.
He adds that achieving better brick strength results in a better- quality product without increasing energy input.
Van Dyk Stene determined that the plant for a design strength of 25 MPa paving brick could achieve a paving brick strength of 30 MPa in 24 hours, with a cement percentage lower than 8% by weight.
Success at Van Dyk Stene
Booysen notes that the Van Dyk Stene plant’s new RE1400 block machine – manufactured by PMSA – as well as PMSA’s imported hardwood pallets, the Kraft Curing system and teamwork from PMSA and Van Dyk Stene, have contributed to a world-class brick manufacturing plant that has thus far achieved a 30% cement saving, also exceeding concrete-strength requirements. This proves that it is possible to lower the cement percentage in bricks without compromising the quality of the end-product.
“The amazing thing about this plant is that we are achieving controlled humidity levels at an average of 90% to 95% , and temperatures of around 30 °C. The plant is not 100% complete yet and we are still doing final adjustments and commissioning,” Booysen says.
Meanwhile, Booysen reveals to Engineering News that negotiations are under way with another new brick manufacturer for PMSA to construct an identical plant by year-end.