Algerian scientists have worked on developing a novel SCSC concrete that could be key to reinforcing civil engineering structures and repairing cracks in ordinary concrete substrates.
Concrete remains one of the fundamental building materials worldwide. Various research projects in recent years have developed stronger compounds thanks to a popular ingredient or with unique properties, such as energy storage, but one challenge remains: a material capable of easily and quickly repairing cracks and other structural damage in buildings.
This could have prevented some of the devastating consequences of the recent earthquake in Morocco or spared British Prime Minister Rishi Sunak this week's scandal involving the closure of more than 150 schools in England due to the risk of collapse. These schools were built with autoclaved aerated concrete (AAAC), a building material that was very common decades ago and has been used in roofs, walls, floors, and cladding despite its disastrous results in ensuring safety.
The current focus is on improving the design and production of concrete repair materials that are more durable, resistant, and cheaper than existing ones to address these types of situations. This is precisely what a team of Algerian researchers has done, recently publishing an article in the Journal of Materials in Civil Engineering detailing the creation of a new type of self-compacting sand concrete (SCSC) that is highly fluid and "exceptionally effective for repairing narrow or hard-to-reach areas."
Repair structures
The increase in the rehabilitation of damaged concrete buildings in recent decades necessitates new strategies and materials to extend the lifespan of their structures. This is not only for the practical reason of preserving what has already been built, but also for environmental reasons, due to "the negative impact that the demolition of damaged structures and the construction of new ones could have," as researchers from the University of Science and Technology and the Materials Laboratory of the Maurice Audin National Polytechnic School in Oran, Algeria, reflect in their study.
In recent years, a wide range of solutions have been proposed for repairing concrete structures, from polymeric and resinous materials to cement-based ones, and these are already being used to rehabilitate hundreds of buildings. However, engineers still feel the need for a cementitious repair material capable of solving problems that arise in very narrow sections or with geometrically complex shapes.
To address this, Algerian scientists have been working on developing a novel SCSC concrete that could be key to reinforcing civil engineering structures and repairing cracks in ordinary concrete substrates. Their main objective was to create a material capable of combining characteristics such as excellent flowability, optimal stability, and acceptable bond strength. In addition to the usual materials used to produce concrete, they included a key ingredient: MEDAFLOW 30, a highly water-reducing superplasticizer (SP) based on polycarboxylate ether with a 30% solids content.
Furthermore, they used a novel pouring method for applying the repair layers and nine different SCSC compositions, which underwent various tests to assess their flowability, permeability, and compressive strength. Additionally, they determined the permeable pore volume and water absorption through immersion tests.
Resistance tests
The most crucial compressive strength tests were conducted at three different times: 7, 28, and 90 days after mixing. These tests aimed to determine the physical and mechanical characteristics of both ordinary concrete and the SCSC concrete separately. Bond strength was also assessed using a tensile strength test and a pull-out test, both of which yielded very favorable results, particularly in thin and narrow sections.
Specifically, this new material exhibited a compressive strength of over 70 megapascals (MPa) and a tensile strength exceeding 3 MPa. For reference, any concrete product with a strength greater than 41 MPa is considered "high strength" and can be used for large-scale projects such as bridges or high-rise buildings.
The main advantage of this new type of concrete is its high fluidity, making it easy to work with and allowing it to flow through heavily reinforced elements, thus filling any cracks in a damaged structure. "SCSC is exceptionally effective for repairing narrow areas, such as the intersection of reinforced concrete elements where the reinforcement bars overlap, and for fixing sections beneath horizontal surfaces, such as bridge decks and other similar structures," the Algerian scientists note in their study.
Furthermore, the ingredients used to manufacture this self-compacting sand concrete, such as water, natural fine sand, recycled aggregates, and sand recovered from limestone waste, are readily available and inexpensive. This makes it easy to produce without incurring excessive costs. "The results and the method used to repair and evaluate concrete layers can be of great help to architects, engineers, and professionals interested in the development and use of cement-based repair materials," the authors of the article conclude.
