Sustainable cement production with the use of surfactant in cement technology

Sustainability is an important concept with respect to the welfare of the world, continuous growth and development. Concrete is one of the most commonly used structural materials in the world. Nevertheless, production of Portland cement, an essential ingredient of concrete, involves significant amounts of CO2 emissions which plays a part in greenhouse effect. Production of a ton of Portland cement, leads to approximately one ton CO2 emission. In addition to the principle of preservation of natural resources, environmental problems related to greenhouse gases play an important role in the sustainable development of cement and concrete industry. It is expected that in the near future it will be more difficult to produce sufficient amounts of Portland cement for the construction industry as the limestone reserves in the world diminish. Portland cement production will come to a halt when the limestone reserves are diminished and the employment in concrete industry will be no more as new construction projects will be impossible to pursue. Therefore, it is necessary to seek sustainable solutions for the cement industry. For this purpose, several measures in motion aimed at sustainable development. Such as advanced preheating technologies (new suspension preheating technology), waste heat recovery (organic rankine cycle and kalina cycle), use of alternative fuels (waste oil and rubber, etc.), use of oxy-fuel combustion, CO2 capture with amine- and ammonia-based solvents, use of industrial waste (fly ash, blast-furnace slag, etc.), and use of grinding aids are taken into consideration. In this study, cement samples were produced using varying ratios of fly ash and cement grinding aids and four clinkers with different compound compositions. First phase of the study involved production of a total number of 20 cement samples, 16 fly ash and grinding aid/strength enhancer added cement samples and 4 reference cement samples, using the Taguchi L16 array. Fly ash was obtained from Seyitömer Thermal Power Plant and used as a replacement for clinker at the ratios of 5%, 15%, 25%, and 35% by weight. During the grinding process, 2 grinding aids and 2 strength enhancer chemical additives were used at the dosages of 500, 600, 700, and 800 g/t. Cements were produced by intergrinding clinker, gypsum and fly ash. In this phase, optimization of the mortar samples was performed with respect to their fresh properties, mechanical properties, dimensional stability, sulfate resistance, water absorption and cost. As a result of the optimization (the 2nd phase), a total number of 7 cement samples, 4 fly ash and grinding aid added cement samples and 3 reference cement samples, were subjected to durability experiments. In the 2nd phase, durability tests such as sulfate (Na2SO4-MgSO4) and acid effect, carbonation, seawater effect, high temperature effect, and alkali-silica reaction effect were performed on the mortar mixtures. The 3rd phase involved SEM/EDS analyses on the cement pastes subjected to sodium sulfate, magnesium sulfate, sulfuric acid, and seawater effects. It was found that decreasing C3A content and increasing C3S content significantly improved grindability. Therefore. C3S/C3A ratio was observed take an important parameter in terms of grindability of clinker. The use of fly ash in hard-to-grind clinkers had a positive effect on the cement properties. Blaine fineness value of the cement increased while average particle size decreased as the fly ash content increased. It was concluded that substitution oh high C3S content clinker with fly ash provides better grindability and high strength. Fly ash ratio was found to be the most effective parameter in terms of early strength. Increasing the fly ash content decreased early age strength. Besides, the cements with higher fineness or smaller particle size expand more, however, the effect reduced with the use of fly ash. Fly ash addition reduced the expansion of the cement due to acid and sulfate effect. MgSO4 caused physical degradation by loss of mass and strength, whereas Na2SO4 resulted in expansion of the mortar mixtures in SEM/EDS analysis, ettringite was detected in cement pastes exposed to sulfate and acid effects. Moreover, Ca/Si ratio of the C-S-H reduced in fly ash added cements. Ettringite was also detected in cement paste samples stored in seawater. For the materials used and tests applied, it was concluded that replacement of 15wt% to 25wt% of clinker with fly ash is the ideal solution. Morever, the combined use of grinding aid admixtures and fly ash in cement production offers great advantages in terms of sustainability, preservation of natural resources and durability.