Dear Colleagues,

Concrete is an incredible human-made material which has been evolving for more than 2000 years and will continue to transform from self-healing to Martian in the years to come. Concrete is the second most used material after water on Earth, and this material may become the best building material in the Solar System.

Concrete was used by the Romans, made from lime, pozzolan, and aggregate. John Smeaton used such material in 1756 to rebuild the Eddystone Lighthouse in England, and several others independently discovered the usefulness of such material to make concrete during the following years. Joseph Aspdin is credited with the invention of Portland cement, which he patented in 1824. He gave it its name because the product of Portland cement and aggregate resembled the stone that came from the Isle of Portland on the south coast of England. Portland cement subsequently came to be manufactured in many European countries and eventually all over the world. It was imported to the United States from England for a number of years before the first American plant was built in Pennsylvania in 1850. Today there are many companies manufacturing Portland cement under many brand names worldwide, and the total production volume is ~4.2 billion tons worldwide yearly in the last 5 years. There are also slag cements, modified Portland cements, and lately, there has been a tendency to use Alkali Activated Materials (AAMs).

The production of AAMs as an alternative to Portland cement started in Germany in 1908. For the following years, its production was mainly focused on the former Soviet Union and China, where cement shortages were experienced which led to the need for alternative materials; alkali activation was developed in both regions as a means of overcoming this problem by utilizing the materials at hand, specifically metallurgical slags. Fundamental research on AAMs has blossomed internationally only since the 1990s, and most of this work has been focused on AAMs microstructure, with little emphasis on the prediction of service life, durability, and engineering properties.

The last decade has brought a splendid innovation into concrete development. It is known that no matter how carefully concrete is designed and mixed or reinforced, all concrete eventually cracks — and those cracks lead to structural collapse sooner or later. As a solution to seal cracks in concrete, several researchers from TU Delft (The Netherlands) and UGent (Belgium) have been working on bio-concrete or self-healing concrete using bacteria. Innovative development has also recently been seen in 3D printing to quickly produce different structures, and this technology can often handle geometries that traditional construction techniques cannot. Traditional concrete is not an environmentally friendly material to make or use and is also impervious; therefore, eco-friendly forms of concrete are currently being developed. Starting in the 1920s, sulfur concrete has been reported to be utilized as a construction material. Various researchers and engineers studied and succeeded in obtaining high-strength and acid-resistant sulfur concretes. In the 1970s, researchers developed techniques to modify sulfur with additives and stabilizers to improve the durability of the product. These days, in response to scientific interest in building on Mars, a research team at Northwestern University (USA) created a form of concrete that can be made with materials native to the Red Planet.

This Special Issue, “Innovative Solutions for Concrete Applications”, aims to provide an overview of current innovative tendencies in concrete technology and structures, which have the potential to be implemented in the industry in the future, covering all recent developments in the construction sector.

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• concrete
• AAMs
• mix design
• waste and byproduct recycling in construction materials
• 3D printed concrete
• real-time monitoring
• structures
• survey