Standing Strong

Steinbeis experts develop cement-free casting compound for industrial floors subject to strong wear and tear

Portland cement has been the most important binding agent mixed into concrete in the construction industry for over 100 years. Over two billion tons of cement are produced every year, and this extremely high output volume comes with a major price tag when it comes to the economy and the environment, primarily because it results in high emissions. Saving resources has become more and more important to the construction industry in recent years – without significant improvements to efficiency, it will be extremely difficult to make construction or housing more sustainable. As a consequence, there is tremendous demand for light but strong materials and composite construction methods. FiberCrete, the Steinbeis Innovation Center based in Chemnitz, has been working on the development, testing, and production of new fiber- and textile-reinforced construction materials and compounds, as well as production technologies. Its main focus lies in material development, design, technological implementation, analysis, and the determination of critical factors. As part of a network project, the Steinbeis experts have now developed an energy-efficient alternative to Portland cement.

The research project is receiving backing from the Federal Ministry for Economic Affairs and Energy as part of the ZIM initiative (Central Innovation Program for SMEs). The Steinbeis experts have been working alongside their partner in industry, Hainspitzer Bauchemie Hand GmbH, to develop a cement-free, fiber-reinforced casting technology. Their solution is called AlkaliTexR and is now ready to launch, providing an alternative to Portland cement for producing mortar systems and concrete parts.

There was already a growing tendency in recent years to save money by using Portland cement composites. These typically contain Portland cement clinker and other secondary raw materials. To meet the Federal Republic of Germany’s climate goals, which entail a 40 percent drop in greenhouse gases by 2020 compared to 1990, simply using composite cements will not be sufficient (cf. Gartner, E. M.; Macphee, D. E.: A Physico- Chemical Basis for Novel Cementicious Binders, in Cement and Concrete Research 2011, 41). Also, due to its low chemical stability at low acidity, Portland cement-based concrete cannot be used freely in all areas. Alkaline-activated binders (AABs) are an interesting alternative for manufacturing concrete and mortar, as they partly deliver superior properties and are capable of reducing greenhouse gases versus Portland cement.

The first step for the project team was to process an optimized mixture of components consisting of reactive secondary raw materials – ground granulated blast furnace slag and coal fly ash – in a pugmill mixer to create an AAB casting mortar. First the binding agent and aggregates were added and then they were mixed for 30 seconds. The mortar was then activated by alkaline, using a mixture of caustic soda and aqueous sodium silicate solution at ambient temperature. Next, alkaline-resistant glass fibers were added. To avoid damaging the vulnerable glass fibers, any further mixing was kept to a minimum and the amount of energy used during mixing was reduced. The AAB compounds were then poured into molds. The compounds were left to settle at ambient temperature for six hours before being removed from the molds. To check the properties of the new AAB casting mortar, the researchers tested representative material samples. The casting mortar falls into a slump-flow category called F1 under DAfStb guidelines (the German Committee for Reinforced Concrete’s directive for the manufacturing and application of cement-bonded concrete and concrete grout). An assessment of compressive and bending tensile strength resulted in values of 47.6 and 5.2 MPa respectively, although these could be raised to 67.5 and 22.9 MPa respectively by including a 3D weave. After 14 days, shrinkage had occurred resulting in a deformation of 0.94 mm/m. A number of measurements identified that this high level of shrinkage deformation was due to continuous restructuring and polymerization in the aluminosilicate gel structures. The pH value of the fresh AAB was 14, and after 14 days reactions had reduced this to 10. To determine the durability of the AAB matrix, the project teams examined frost resistance, water permeability, and acid resistance.

 

After the positive testing in theory, it was then time to conduct tests in real application. “We took a number of industrial floors measuring between 15 and 20 square meters as our reference points, and some of the floors had serious surface damage. Our aim was to restore the concrete surfaces by using self-flowing AlkaliTexR,” explains Dr. Sandra Gelbrich, director of the FiberCrete Steinbeis Innovation Center. The renovations involved using short fiber-reinforced and textile-reinforced AAB setting compound with varying degrees of thickness of between 8 and 20 millimeters. To prepare for testing, the dry and liquid ingredients were poured into two separate containers using gravimetric dispensing. Mixing was carried out at different intervals in a portable pugmill mixer, which was specially developed for the AABs, first dispensing the liquid components and then adding the dry ones. After mixing the ingredients for three minutes, the pugmill mixer was emptied and the fresh AAB was poured in small quantities onto the floor. Within two hours of the renovation work, the new floor could be walked on and was strong enough to bear a load. The industrial floors repaired with the AAB showed no sign of cracking or surface defects.

The experts working on the consortium project believe that alkalineactivated binding agents are an interesting alternative for partially or entirely replacing Portland cement in the production of mortar solutions and concrete elements. AlkaliTexR consists of an alkaline-activated bonding agent with integrated textile reinforcements and has been adapted for industrial floors. It delivers high levels of mechanical and chemical resistance and is extremely durable. The solution developed by the experts has already been patented and the team is also going full steam ahead with other developments. Given the major potential of fiber-reinforced alkaline-activated binding agents, the Steinbeis experts are currently working on other AlkaliTexR products for restoring and reinforcing surfaces subject to chemical influences.

Contact

Dr.-Ing. habil. Sandra Gelbrich, Henrik L. Funke
Steinbeis Innovation Center FiberCrete (Chemnitz)