With the construction sector in East Africa seeing an upswing, CHRYSO East Africa has grown its offerings to the market while ensuring its admixture solutions are targeted at local conditions.

According to Graham Dean, CHRYSO’s Business Development Director Eastern Africa, the region’s growing investment in construction projects is evident in countries like Kenya, Tanzania and Uganda. While infrastructure development such as roads and railways are mainly driving this growth in Kenya, it is Tanzania’s mining industry and Uganda’s oil sector which are becoming more significant.

“As a key construction product, concrete uses natural materials which are locally sourced,” says Dean. “This might include cement produced from limestone quarried around Nairobi, pozzolana to modify different cement types or quarried aggregates and crushed sands. To achieve the best results in concrete, it is important to understand the variations in what Mother Nature provides to us as raw materials.”

He highlights that concrete admixtures which have been well proven with materials in South Africa, for instance, may not necessarily perform to the same levels with concrete materials from Kenya. Accommodating these variations has required considerable investment in research and technical facilities in East Africa, to ensure customised admixture solutions.

“To resolve the performance differences between regions, CHRYSO set up a concrete laboratory in Nairobi where we can modify existing formulations,” he explains. “This allows us to design bespoke admixtures for customers, based on their specific requirements and the local materials going into their concrete.”

With its Nairobi office established almost 10 years ago, CHRYSO has developed the locally based experience and infrastructure to become a trusted partner in the concrete space. The company supplies its admixture solutions not only to large construction companies, specifiers and developers, but also to readymix plants, manufacturers of precast products and specialist applicators of decorative concrete.

As the negative environmental impact of sand mining falls under the spotlight in certain East African countries, CHRYSO is also contributing to more responsible practices in the concrete segment.

“The uncontrolled mining of river sand for concrete in many areas has led to concerns at government level, and an expectation that this practice might be banned in future to prevent further damage to the natural environment,” says Dean. “We have promoted our Quad range to raise awareness in the construction industry about alternatives to river sand.”

CHRYSO uses its in-house polymers in the Quad range of products to accommodate the use of challenging sands, including too little or too much fines, swelling clays or irregular shapes. Being able to use lower quality sands can drive down procurement costs, and can also reduce the carbon footprint of a given concrete where these alternative materials are closer to site.

“We have also taken a leading role in the supply of additives to cement producers, with our in-depth understanding of cement production technologies,” says Dean. CHRYSO has been supporting cement producers to reach their sustainability goals, as cement manufacture is a leading contributor to carbon dioxide emissions. The company’s innovations allow more efficient clinker grinding, reducing power consumption in this energy intensive process. 

The additives permit increases in the compressive strength at the initial, mid-term and later ages. The resulting enhanced performance can meet specific market needs such as reducing cement fineness or lowering unit production costs. The clinker factor can also be reduced by using increased levels of supplementary cementitious material (SCMs) while retaining cement performance. CHRYSO additives can be used for the grinding of most cements in all types of grinding systems, including those with ball mills, roll presses, and open and closed circuits, as well as horizontal roller and vertical roller mills.

CHRYSO is able to develop specialised products for customers, to suit their applications. A customer in Mombasa, for instance, needed a solution for the use of coral limestone as a bulking agent in cement production.

“Coral limestone is a notoriously difficult material to blend effectively into cement,” he notes. “Through extensive trials for the customer, CHRYSO East Africa was able to formulate a solution by finetuning one of our products; the result was a solution which overcame the customer’s challenge and is now being regularly used.”

With South Africa’s winter season on its way, many concrete users will know that slower curing times could derail their contract or production schedules, but accelerating admixtures – or accelerators – are available to solve this challenge.

With the country’s generally temperate climate, it is easy to forget that many provinces and neighbouring Lesotho regularly experience sub-zero temperatures, points out Hannes Engelbrecht, Concrete Business Unit Director for Domestic and Sub Saharan Africa (SSA) at CHRYSO Southern Africa. Temperatures do not even need to reach freezing point; the concrete hydration process slows down steadily as temperature drops and actually stops when it goes below about 5 degrees Celsius.

A significant amount of current concrete construction – especially for wind turbine bases and foundations for solar photovoltaic infrastructure – is, in fact, taking place in provinces like the Northern Cape and Eastern Cape where temperatures fluctuate widely. Efficient stripping time of formwork is crucial in allowing these projects to meet their stringent deadlines to complete construction and start delivering renewable energy.

“Low temperatures create a range of problems for contractors and concrete product manufacturers,” says Engelbrecht. “Most projects in today’s world need to be delivered on a fast track basis, so there is no room for slow concrete curing to hold up the schedule. Similar constraints apply in the manufacture of precast products, where production must simply keep up with customer orders and delivery deadlines.”

He highlights that precast product manufacturers can use a combination of super plasticisers and accelerators to speed up their stripping times and reduce the storage space needed for products to cure. Accelerators work during the first 18 hours of the concrete’s curing time to ensure efficient hydration required to depalletize. Should temperatures be lower than freezing point, this makes the concrete strong enough to resist the expansion of water as it freezes – so that the concrete will not crack.

Patrick Flannigan, Technical Manager of the Concrete Business Unit at CHRYSO Southern Africa, explains that there are two categories of accelerator – chloride and non-chloride. While chloride-based accelerators are usually the first choice, they cannot be used if there is steel in the structure or where steel reinforcing is present due to the risk of rust, corrosion and degradation.

“If there is steel reinforcing in the concrete, then a non-chloride accelerator must be selected,” says Flannigan.

Regarding the use of accelerators in readymix concrete that must travel varying distances to site, he points out the accelerator is best applied once the readymix has arrived on the customer’s site. After it is added to the concrete in the mixing truck, it needs to be thoroughly mixed for 5 to 10 minutes before being poured. The admixture gives operators a good 30 to 40 minutes of workability before the accelerated hydration begins, depending on the type of concrete mix.

Another growing benefit of accelerators has emerged as a result of the global sustainability drive, he says, as cement producers, contractors and other customers aim to reduce their carbon footprint. This trend has seen the increased use of extenders such as fly ash and granulated slag in cement.

“The fly ash and slag only start working once there is an initial hydration of cement,” he says. “This means that the early strength of a concrete mix will be delayed when there are extenders added.”

The accelerating admixture overcomes this initial delay in the early setting, allowing users to achieve their sustainability goals without compromising on speed of the curing process.

CHRYSO Southern Africa, located in Jet Park, Johannesburg, maintains two state-of-the-art laboratories that form the backbone of its operations. These facilities, the Quality Control and Research and Development Laboratory and the Concrete and Cement Laboratory, support the company’s customer across all industries by ensuring quality, safety and efficiency.

Mpumi Mlalazi, R&D Manager at CHRYSO Southern Africa, explains that the Quality Control and Research and Development Laboratory has a multifaceted role. “Firstly, it ensures quality assurance and compliance with industry standards and by doing so, strengthens our reputation of reliability and trust.”

“By driving process improvement initiatives, we enhance our efficiency and effectiveness and through this our laboratory plays a crucial role in facilitating innovation and new product development, ensuring we stay at the forefront of industry advancement,” Mlalazi says. “The laboratory also offers problem-solving expertise to our customers, ensuring issues are quickly identified and rectified, adding value to their bottom line.” 

The Concrete and Cement Laboratory also has several functions. It conducts comprehensive material testing and analysis, ensuring the quality of cement and concrete chemicals used in industry. Mlalazi explains that by evaluating strength and durability properties, CHRYSO Southern Africa ensures that the materials used can withstand the demanding conditions of the particular application where these materials are being used. 

“Our team also performs chemical analysis for compliance and optimal performance, and the laboratory engages in research and development for new chemicals and formulations. We also explore specialised applications and sustainability considerations, and doing this ensures our operations remain environmentally conscious,” she says. 

By harnessing the capabilities of these laboratories, CHRYSO Southern Africa reaffirms its commitment to delivering a customer focused service, meeting the highest quality standards and addressing the specific needs of its customers in Africa. 

Mlalazi affirms that the CHRYSO laboratories undergo annual audits to maintain its ISO certifications, further demonstrating commitment to quality, environmental responsibility and safety. “Our ISO 9001 certification is a testament to the emphasis we place on quality management principles such as customer focus, the involvement of top management, a process-driven approach and continuous improvement. Our ISO14001 certification emphasises our dedication to measuring and actively improving our environmental impact, demonstrating to company management, employees and external stakeholders our commitment to environmental responsibility.”

Once again, CHRYSO is the first out of the starting blocks, having introduced its CHRYSO® Quad range of concrete admixtures to the market in 2022 – helping customers to promote sustainable practice in their use of challenging sands.

According to Patrick Flannigan, Technical Manager in the Concrete Business Unit at CHRYSO Southern Africa, the use of crusher or manufactured sand in construction has been prevalent for many years as it is a cost effective and more readily available alternative to natural sand.

“There have, however, been issues with grading which often prompts contractors to supplement with natural sand from sources such as rivers and dunes,” he explains. “This is where the challenges lies with less availability of natural sands which increases costs as well as the presence of clays which means that less of this material can be used or it has to be excluded completely.”

“Our CHRYSO® Quad range allows customers to reduce their use of natural sand while making better use of crusher sand, without compromising the quality of their concrete mixes, and successful laboratory trials have already been concluded with customers in various market segments are already realising the benefits,” Flannigan continues.

“Working with customers such as contractors, readymix suppliers and precast manufacturers, CHRYSO is making significant contributions to industry sustainability and reduced carbon footprint,” he says.

He highlights that using less natural sand gives the industry a lower environmental impact on sources like rivers. Where natural sand is still being used, CHRYSO® Quad CLEAR® (Clay Enabling Admixture Response) allows a wider choice of sources – even challenging sand that contains swelling clay. This can allow contractors to source from locations closer to site, reducing the carbon footprint and cost of transporting sand over a long distance.

“The challenge is that swelling clays absorb newer generation plasticisers, thereby preventing them from delivering benefits such as water reduction or slump retention,” he says.

CHRYSO Southern Africa also offers the quick and innovative CHRYSO® CLEAR Test to identify where these swelling clays could present a problem for concrete users. Where they are identified in the source material, CHRYSO® Quad CLEAR® can be added as a liquid to the relevant plasticiser.

Another important contribution to sustainability in the construction and concrete manufacturing sectors is CHRYSO® Quad GRAFT® (Gap Gradation Fixing Technology), he notes. This can solve the challenge of an excess or lack of fines in source material – which often occurs in crusher sand.

“The industry is seeing the environmental benefit of moving away from natural sand and more toward crusher sand, but this product often has varying levels of fines,” he says. “In the past, this could have compromised the performance of concrete, but CHRYSO® Quad GRAFT® now solves this challenge.”

Contractors are getting closer to the key objective of the Kariba Dam Rehabilitation Project – to reshape the plunge pool below the dam wall and arrest any further erosion.

Concrete is a central element of this world class engineering project, and CHRYSO® Southern Africa’s Zambian distributor, Mart Solutions Ltd has been one of the key suppliers of construction chemicals to main contractor Razel-Bec since the very beginning of the project. This collaborative effort over the past several years has ensured the project’s steady progress. With the aim of stabilising the plunge pool at the foot of the 138 m high dam wall, the project is using vast quantities of concrete in a range of applications.

The total volume of concrete used – which includes the coffer dam and underwater works as well as excavation – is almost 26 500 m³. At the coal face is Mart Solutions Director, Martie Coulson.

“Among the first challenges we faced was in the construction of piers for the temporary coffer dam, where concrete had to be poured underwater to create a foundation,” says Coulson. “Difficulties in finding bedrock for piers 7, 8 and 9 – as well as for the dam’s right bank – meant that 22,000 m³ of concrete had to be placed underwater.”

This arduous process – which took six months and was completed in September last year – involved pumping concrete to 25 m deep, with divers handling the 125 mm diameter pipe to place the concrete. Adding to the complexity was the movement of water from the nearby Zimbabwe’s hydro-electric turbine outlet, which exacerbated the ‘wash’ off the concrete into the surrounding water.

“This raised the risk of the cement being washed out of the mix, leaving the aggregate behind as well as further reducing visibility for the divers,” she explains. “The CHRYSO® Aquabeton product played a critical role as an anti-washout admixture that increases the cohesion of the concrete mix.”

This allowed the placement of a concrete base for the three piers, measuring some 15 m wide and 20 m deep. Another important aspect of the project is repairing a fault in the rock at the foot of the Kariba dam wall. Stitching of the fault will include the use of 40 mm anchors in the rock with CHRYSO NS Grout added to a concrete mix. In addition, 20 mm, 25 mm and 32 mm anchors will be used and will be secured with a.b.e.® dura.grout supplied by Mart Solutions Ltd.

“Some 7 071 m³ of specialised concrete will be used for the large 90 m high, 45 m wide and 2,5 m thick wall which will be built in front of the fault as a protective shield,” she says. “This will be fixed onto the 12 m long, 40 mmdiameter anchors in the wall, which will in turn be secured 10 m into the rock.”

A combination of CHRYSO® Omega 162 and CHRYSO® Fluid Optima 206 will be used in conjunction with densified silica fume and fly ash in the concrete mix for the wall – to assist in preventing the temperature rise in the concrete during  placement and to avoid cracking. This is important due to the high ambient temperatures of up to 40 degrees Celsius.

“We have been running laboratory trials for three years to ensure that the concrete mix design will meet the standards specified by the engineers for the wall to ensure that the concrete will remain below 55 degrees Celsius during placement,” she explains.

As part of the preparation of the concrete, therefore, a chiller plant will be cooling the water and aggregate before it is added to the mix. In another aspect of the project, Mart Solutions is providing the anchors to secure the safety nets which are being installed against the risk of rockfalls in the excavation, as well as a.b.e.® dura.grout for securing the anchors. This non-shrink cementitious grout quickly develops placeable consistency and remains cohesive. CHRYSO Jet 30 is also being supplied for shotcreting, mixing with concrete as it is sprayed to ensure adhesion to the rock surface.

“As the coffer dam is dewatered, the contractors are able to start micro-blasting to clear rock from the plunge pool,” she says. “The walls must then be secured to prevent any rocks from falling.”

Mart Solutions has already provided the CHRYSO® Omega 162 superplasticer for building the coffer dam piers. Ranging from 250 tonnes to 700 tonnes in weight, these piers measure 5,5 metres tall.

“The new generation CHRYSO® Omega 162 high range water reducing plasticiser played an important roleto reduce water demand, thereby increasing the concrete’s durability,” she says. “It also improved the concrete’s cohesion and lowered its viscosity, for better homogeneity and off-shutter finish.”

CHRYSO® Omega 162 allows concrete to exhibit extended workability characteristics, while CHRYSO® Fuge B – a pore-blocking permeability reducer for mass concrete – was used in the coffer dampiers to prevent the penetration of water under pressure.