Bumper growth is unquestionably underway in Africa’s cement, concrete and construction industries. In 2014, Africa construction sector attained a growth of 46.2%, with a total of 322 different collected projects in all sectors of construction, representing a total value of US$ 222,677 million.
The concrete industry in Africa is therefore full of opportunities, that surely need to be built on. But the engineering of concrete structures is a continuous developmental process. Invention and development of new construction methods place even higher demands on building materials. In Africa, concrete producers face this technological challenge daily alongside other factors such as economy, ecology, raw material and energy costs as well as increased logistical complexity.
Designing an entire watertight building from the basement to the roof requires the development of solutions for the widest range of applications, offering practical implementation as well as permanent protection. This is better said than done. Indeed, alongside water, building structures are exposed to a broad range of forces and strains. It starts with mechanical stresses resulting from the type of construction and can extend to various external attacks, such as extreme hot or cold temperature conditions, aggressive water or other chemicals, continually rolling, abrading or pulsating strains on surfaces, etc. They all place enormous stresses on structures as a whole and on building materials. That is why there has been continually increasing demands for the concrete quality, mainly its durability.
Huge advances in concrete technology have brought about the production of many different kinds of concrete, with better implementation, composition and resistance of its materials. Admixtures and additives have played the greatest part of such technical progress. Indeed, concrete technologists have always understood that the two most important functions of “water” in producing quality concrete are almost diametrically opposed. Technological advances in chemical admixtures made it possible to achieve both of these requirements, together at the same time, and practically on the job site. Added to the 3 main components of concrete (binder, water, aggregates), they bring several innovative options to concrete mix design. Some of their major characteristics are:
- Shortening the setting time of concrete mixes
- Making them waterproof
- Increasing their strength
- Reducing the water content of the mix
- Maintaining or even improving the consistence (workability)
With that, all participants in the construction process get the desired achievement of sufficient early strength to allow formwork removal as quickly as possible, whether on construction sites or in production of precast concrete. In addition, lower water / cement ratios result in dramatically enhanced durability, induced by remarkably low concrete permeability. Although the specific technical requirements for the concrete differ for each project or applications, the steps to achieve constant and consistent concrete quality remain the same, and consist in the right planning and preparation of the concrete works, whether production, placing or curing. These are all crucial considerations for the successful use of this fantastic building material.
A high water demand to achieve workability for optimum placing and compaction, a low water demand for optimum strengths and durability! Does the mix design of concrete is more than merely a technical issue. It inevitably also deals with finding cost-efficient raw materials and developing ecologically friendly concrete mix designs. In the past the driving factor for concrete mix design was to develop a concrete mix that complies with standards and fulfills the requirements at minimum cost. With changing ecological specifications and restrictions, as well as the challenging economic context, the production of resource-friendly and cost-efficient concrete mixes is becoming more and more important, and with this the sustainable use of raw materials is needed.
Final products can be optimized with regard to local market requirements to yield the best cost-performance solution, by performing product development in the local area by the local branch in their own laboratories. The products can thereby assessed and adapted to suit local conditions, regulations and production requirements. This process facilitates cost optimization for local manufacturing and competitive market pricing. The durability of the concrete is also a particularly important topic when designing a cost-effective concrete structure. Improved durability results in prolonged service life of concrete structures and elements, lower costs for maintenance and refurbishment works, as well as less repair work. In addition, a highly flowable concrete helps simplify the entire construction process.
The speed of the whole construction process is gaining importance, because fluid concrete implies fast casting, fast discharge of mixer and truck, easy placing and compaction, as well as good surface finish, which all result in overall reduced effort and time saving. Subsequently, the project will benefit from fast stripping time with efficient formwork operation and cost optimization of material, energy, logistics and manpower.
From the owners’ perspective especially the main focus lies in the investment and maintenance cost in combination with the speed of construction. This mostly implies high concrete durability and quality, slender dimensions of structural members, as well as application of innovative fast construction methods To achieve the aims listed, a technological challenge will be powerful water reduction in the concrete mix, which will result in increased impermeability leading to higher quality and durability.
As for the contractors, they carry out the last part of the process onsite, it should be as easy, fast, safe and cost efficient as possible. Therefore they have highest interest in concrete properties directly influencing the construction process. This direct link mainly means sufficient workability offering easy and fast placing and compaction, time saving, short stripping times and fast turnaround of formwork, as well as greatly improved working conditions.
A concrete construction designer is constantly looking for new construction methods and technological possibilities in order to make full use of all different material properties leading to cost efficient and timely construction. Outmost importance is attached to appearance and aesthetics, the designer’s calling card. Furthermore, resource friendly design methods and ecologically sustainable building materials have proved to be growing concerns to designers’ minds. As it happens, the ability to resist the ingress of pollutants enhances the durability of concrete, thereby guaranteeing the engineering properties of the concrete structure for an extended period.
Admixtures in particular offer some technological solutions, such as impermeability of the hardened concrete facilitated by outstanding water reducing capability, significant shrinkage crack reduction, excellent flow ability producing smooth, dense surfaces, development of cost efficient, sustainable concrete mixes, as well as design of watertight concrete, and frost and freeze/thaw resistant concrete.
Having said that, formwork preparation plays a major role for the final appearance of the concrete surface, the challenge is to prevent adhesion of the hardened concrete on the formwork and ensure easy cleaning of it. This can be achieved with correct application of a suitable mold release agent, which additionally leads to smooth and dense concrete surfaces improving the durability as well as the aesthetical appearance of the concrete surface.
The following requirements are specified for the action of mold release agents, both in situ/cast in place situations, and for precast concrete applications: The concrete industry cannot do without release agents. When correctly selected and used with the right formwork and concrete quality, they contribute to visually uniform and durable concrete surfaces. Inappropriate or wrongly selected release agents, like unsuitable concrete raw materials and compositions, can cause defects and faults in and on the concrete surface.
The proper design and material volume calculation leads to the fulfillment of all relevant standards, improves the quality of the concrete produced and opens door to more economical solutions. This white paper was meant to offer an introduction to concrete and its application as well as an overview of the economic and production benefits in using the most important building material, that is concrete.
