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Sunday, 22 January 2017
Raw materials & technologies, Raw materials

“Highly specialised products”: Interview on construction chemicals

Friday, 17 April 2015

Complex mixtures of materials require a knowledge of construction and cement chemistry, explains Dr. Wolfram Schmidt, Federal Institute for Materials Research and Testing (BAM).

Dr Wolfram Schmidt, BAM

Dr Wolfram Schmidt, BAM

Understanding cement binder systems, in particular their rheology, interactions and influences, is a speciality of Dr. Wolfram Schmidt, BAM. He discusses in this interview how far removed modern cements are from Portland cement, and explains the influence of biopolymers and gypsum.

What cement projects are you working on now?
Dr Wolfram Schmidt: A great many projects, all of which inevitably lead back to the topic of the binder concepts of the future. A main focus of my research is on admixtures for controlling processing properties and I’m currently working to plug the knowledge gap between the natural sciences and engineering. Cementitious materials, especially mortar applications, are now highly specialised products that possess excellent properties and boast a plethora of different active groups for maintaining precise control over workability, strength development and durability. The problem is that the various components interact with each other in such a complex way that such systems often fail to be as rugged in use as expected. In other words, tiny variations in the underlying conditions can have a huge impact. I’ve set myself the goal of gaining a better, more integrated understanding of these effects. Which is why I spend a great deal of time studying interactions between rheology-modifying polymers and hydrating cement in the period of time that elapses between addition of water and setting. This is an area where biopolymers, too, play an important role.
I’m also doing extensive research into new binders based on large amounts of alternative materials. This aspect has global implications, because there is no such thing as a universal binder system. Binder systems should always be tailored to local conditions and supply chains. Consequently, we are also cooperating very closely with partners in Africa. One of the things we have done there is to create a pan-African inter-laboratory test set-up for checking the quality of cements.

Let’s talk in more detail about the project covering the various aspects of controlling the processing properties of modern concretes. Which technological innovations are being deployed in the search for a solution?
Schmidt: Modern concrete technology utilises highly complex active ingredients. Workability has become hugely important and so too has the interplay between construction chemicals and cement chemistry, which is extremely complex. Pure Portland cements now account for only about 30% of the market in Germany and many other countries. Meanwhile, over the past few decades, the construction chemicals industry has delivered a steady supply of outstanding new developments that are increasingly finding application on site. At the moment, superplasticisers based on polycarboxylate ethers represent the state of the art. These polymers offer unbeatable versatility, but you need to understand that the path leading to innovations in construction with cementitious materials is not necessarily to be found in a plethora of new formulations. On the contrary, it lies in merging the expertise found in the areas of construction chemicals and cement chemistry. Whoever masters these two components holds the key to innovation.

Speaking of technological innovations, which will also feature at the ECS, what do you consider to have been or to be the major milestones in cement technology?
Schmidt: A major milestone in cement technology in the past was the realization that reduced-clinker cements can still be good cements. Another, very recent milestone has been the growing realization that cements can be tailored. And a very important future milestone will be reached when that knowledge can be implemented in a global context. The ideal cement technology, eg raw materials, manufacture, formulation, application, will defy description in a standard, and nor should it be based on a technology that suits other countries or regions. Good cement technology is highly individual and regional.

And where do you think there is an urgent need for solutions – and why? Realistically speaking, what are the prospects of finding these anytime soon?
Schmidt: The biggest problem afflicting construction with cementitious binders is fluctuations in composition. By its very nature, cement manufacture is a mass-production process and so it is not right to blame the cement for modern construction materials’ lack of ruggedness. Cement is and remains the most important component, and cement manufacturers do their best to keep the quality steady while endeavouring to make production as ecologically sound as possible. The pertinent standards are being observed in this regard. The problem of modern construction materials, however, lies more with the high importance of the superplasticiser – its mode of action depends considerably on the gypsum added to the cement to act as set-controlling admixture. In the past, this relationship did not matter. Which explains why the effects of the gypsum and interactions with organic polymers are not adequately covered in the cement standard. If in the future we succeed in being able to make better predictions about how the main actors – cement and superplasticiser – interact, we will have made great progress. It is not only at the BAM that researchers are working to gain a better understanding of these processes, but also around the world. And so I am confident that we will see a great many innovations in cementitious construction methods over the next ten years. We are only just at the beginning.

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