Cement production accounts for 1650 million metric tons of yearly global CO2 emissions [1], making it one of the largest contributors to worldwide CO2 emissions. One pathway to reducing CO2 emissions associated with concrete construction is through the use of alternative cementitious materials and binders (ACMs) such as calcium sulfoaluminate, calcium aluminate, and alkali-activated binders. These materials often require lower production temperatures than ordinary portland cements (OPC) and have lower calcium contents, reducing the emissions associated with CO2 released from calcium carbonate during calcination. Most ACMs are not new materials, but past uses have been primarily limited to small-scale applications such as pavement repairs and little field experience exists concerning their long-term durability in highly-trafficked structures such as pavements and bridge decks. This paper presents outcomes after the first year of a U.S. Department of Transportation effort to increase understanding of how to best utilize ACMs in new transportation infrastructure throughout the U.S. and presents the challenges in evaluating the durability of these materials using laboratory testing methods developed for use with OPC concrete. These concepts form the foundation for continued research and broader implementation of ACMs in transportation infrastructure.

In the prospect of reducing CO2 emissions and landfilling of waste materials, the preparation of sustainable mortars by alkali activation was studied. According to EN 1504-3:2005, geopolymeric and cementitious mortars belonging to different strength classes (R1 ≥ 10 MPa (1450 psi), R2 ≥ 15 MPa (2175 psi) and R3 ≥ 25 MPa (3625 psi)) were tested and compared. Geopolymers were obtained with fly ash or metakaolin and a blend of sodium silicate and NaOH (or KOH). Mortars were tested in terms of workability, dynamic modulus of elasticity, drying and restrained shrinkage and porosimetry. Durability was also investigated in terms of water vapour permeability, capillary water absorption and corrosion of possible embedded rebars during the curing period and wet-dry cycles in 3.5% NaCl solution. Results showed that geopolymers are subjected to higher drying shrinkage but lower restrained shrinkage than cementitious mortars. Water vapour permeability was higher in geopolymers and capillary water absorption was lower especially in fly ash geopolymers than those of cementitious mortars. During the first month, the high alkalinity of geopolymers extends the active state of both black and galvanized steel bars. However, when exposed to chlorides, fly ash geopolymers offer a higher protection to reinforcements than cementitious mortars.

The effects of substituting 5-20% fly ash for slag and adding 0.10~0.30% polypropylene fiber on the physical and mechanica1 properties, shrinkage and cracking behaviors, water permeability and porosity of alkali-activated ground granulated blast furnace slag cement paste and mortar are studied. The results show that replacing 5-15% fly ash for slag in the alkali-activated slag cement paste and mortar increased the flexural strength, though the compressive strength were slightly decreased. When the replacement of fly ash for slag was increased to 20%, both the flexural and compressive strengths of the paste and mortar begin to decrease. The early shrinkage and cracking were reduced by the fly ash replacement. Adding 0.10~0.30% polypropylene fiber decreased both the flexural and compressive strengths, whereas the shrinkage, especially the cracking of the alkali-activated slag cement was greatly reduced.

Concrete is the most versatile construction material. However, the image of concrete looks often one of something non-friendly from an environmental point of view. Further developments, “green chemistry” and new techniques, should continue to be introduced into the cement and concrete industry. This will provide distinct alternatives to OPC dominating inside cement market. Simultaneously new scientific and technological breakthroughs are required. One of such additional strategies is based on advanced concrete technology concepts, which enables the reduction of the quantity of cement used in concrete, by combining fillers and various admixtures. Another strategy is based on a new design of the structural component, to evaluate the use of different materials and to achieve an overall reduction of the environmental impacts. This strategy highlights Life Cycle Analysis and Design, Performance Standards for Durability, Environmentally Driven Design and the role of the reinforcement, because the conventional steel reinforcement contributes to environmental footprint as much as the cement in the concrete. Composite materials, including polymer composite reinforcement, non-metallic fibers and the external reinforcement for repair and strengthening, would be widely used in modern construction. Additional benefits of synergy between these different solutions might be realized leading to reduction of more than 50% of environmental load.

Metallic soaps are salts from long chain fatty acids and they are popular as waterproofing due to their low cost and effectiveness. A detailed investigation on the mortar specimens made with different chemical additives based on Na oleate, Ca stearate – Na oleate, Al stearate and Ca - Na laurate has been performed. The additives analyzed present a different mechanism of action: Na oleate has a strong effect on the development of mortar microstructure while Al stearate or Ca - Na laurate leaves the microstructure very similar to that of the reference samples. The experimental evidences, by measuring the porosity, the water absorption, the mechanical properties and the morphology, confirm these internal structures in the mortars.