The transport properties, i.e. microstructural behavior and mechanisms related to water and ionic transport within the pore network of cement-based materials can be considered as an indicator for durability and to predict service life of concrete structures. Hence, the investigation of ionic transport is very important to asses ionic diffusion and ionic migration that potentially affect microstructural development of the bulk cement-based matrix. External electric fields are commonly accelerating ion (and water) migration. Numerical works on simulation of these phenomena have been reported, however, most of them consider only a constant ionic diffusion coefficient. This paper deals with the application of the Poisson-Nernst-Planck equations to simulate ionic transport in cement-based systems exposed to external electric potential by considering time dependent diffusion coefficient. The simulation involves solving the equation of mass conservation of individual ionic species coupled with electrostatic potential. Profiles of ionic concentrations and ionic distribution in cement-based systems are presented and discussed.

This work deals with the effect of the concentration of microsphere of silicon oxide (MS) in SBS-modified asphalt.

A series of blends having 2, 4, 6, 8 and 10 % w/w of MS were prepared from a SBS-modified asphalt having 3 % weight/weight of SBS and known amount of MS. Samples were characterized by fluorescence microscopy, to get an idea of the polymer distribution in the blend; and by conventional tests such as penetration, soft point, density and viscosity, to investigate on the thermo-mechanical resistance of such a blends. It was observed that an increase in the MS resulted in a decreased of the soft point and density, an increased the viscosity, and did no affect the penetration of the sample. Therefore, it was concluded that SBS-MS-modified asphalt is an interesting material for producing polymer-modified asphalt layers.

Portland cement is synthesized from a mixture of limestone and clay at high temperature (1450 °C) via a conventional process (solid-phase synthesis), in which partial fusion of raw materials and the formation of clinker nodules are produced. The clinker is mixed with a small percentage of gypsum and ground together to make the cement. This synthesis process holds the cement industry accountable for 5–8% of global anthropogenic CO2 emissions. The production of a ton of cement emits between 0.62 and 0.97 tons of CO2 into the atmosphere, depending on the processing plant. Furthermore, the use of fossil fuels in cement production is another important factor in the environmental impact of this industry. The production of 1 ton of clinker consumes approximately 5.86 GJ per tons of clinker produced in wet processes and 3.35 GJ per tons of clinker produced by dry process. Some researches have reported the possibility to obtain silicate and aluminate cements by alternative synthesis methods, which optimize both time and temperature, such as Pechini method, sol-gel method and microwave assisted method. The combustion methods, another alternative, are chemical redox processes in which the use of chemical precursors and organic fuels at high temperature generate a self-sustaining fastwave. The said wave is characterized by the fact that once the initial exothermic reaction starts, it generates a reaction wave (0.1–10 cm/s) at high temperature (1000–3000 °C) that propagates, in a self-sustaining way, through the heterogeneous mixture which leads to the formation of the solid material. For this reason, and the irreplaceable role of cement in the construction industry, this paper shows the advances in the production of silicates, similar to those found in the Portland cement, by combustion synthesis method.

This paper shows the production of calcium silicates similar to the silicates of Portland cement, by combustion synthesis. Thermal analysis and XRD techniques were used to compare the syhthetized silicates with alite and belite of Portland cement.

In the early 1970s, experts predicted that the practical limit of ready-mixed concrete would be unlikely to exceed a compressive strength greater than 90 MPa [1]. Over the past two decades, the development of high-strength concrete has enabled builders to easily meet and surpass this estimate. The primary difference between high-strength concrete and normal-strength concrete relates to the compressive strength that refers to the maximum resistance of a concrete sample to applied pressure. Although there is no precise point of separation between high-strength concrete and normal-strength concrete, the American Concrete Institute defines high-strength concrete as concrete with a compressive strength greater than 45 MPa. Manufacture of high-strength concrete involves making optimal use of the basic ingredients that constitute normal-strength concrete. When selecting aggregates to obtain high-strength concrete, we consider strength, optimum size distribution, surface characteristics and a good bonding with the cement paste that affect compressive strength. Selecting a high-quality Portland cement and optimizing the combination of materials by varying the proportions of cement, water, aggregates, and admixtures is also necessary. Any of these properties could limit the ultimate strength of high-strength concrete. Pozzolans, such as fly ash and silica fume along with silicic acid, are the most commonly used mineral admixtures in high-strength concrete. These materials impart additional strength to the concrete by reacting with Portland cement hydration products to create additional Calcium Silicate Hydrate (CSH) gel, the part of the paste responsible for concrete strength; finally the most important admixture is polycarboxylate ether as super plasticizer. It would be difficult to produce high-strength ready-mixed concrete without using chemical admixtures. In this paper we study the use of high performance concrete (HPC) to obtain very narrow strong pre-fabricated elements for water conducting channels.

Deterioration of concrete structures, together with corrosion of reinforcing steel due to the action of microorganisms, is known as Microbiologically Induced Corrosion of Concrete (MICC). The activity of microorganisms can initiate and further accelerate both steel corrosion and cement-based matrix degradation in reinforced concrete structures. The mechanism is related to initial surface colonization and further bio-products (and aggressive substance respectively) penetration into the bulk concrete matrix, reaching the reinforcement level. Common knowledge is that bio-deterioration-related infrastructure degradation, maintenance and repair have a significant economic impact worldwide. However, due to the complexity of all related mechanisms, a durable and feasible solution is still to be achieved for the engineering practice. This paper briefly points out main bio-degradation related mechanisms for concrete, steel and reinforced concrete structures and presents results on the electrochemical response of carbon steel in simulated environment under biotic and abiotic conditions.

This work presents the electrochemical behavior of Ag/AgCl electrodes (chloride sensors) in cement paste environment, monitored over a period of 180 days via open circuit potential (OCP) readings and electrochemical impedance spectroscopy (EIS). The EIS response indicates modification of the sensors’ morphology, in particular alteration of the AgCl layers, as a result of continuous chloride penetration into the bulk matrix towards the vicinity of the sensor/cement paste interface. A gradual shift to more cathodic OCP values and stabilization at approximately -1mVSCE to 2mVSCE was observed at the end of the test, reflecting chloride content of 820mM to 930mM in the pore solution surrounding the sensors, which differs 5-10% from the chloride concentration in the external solution. The water soluble chloride content in the cement pate, as destructively measured wet chemically by Volhard method and photometry, was in the range of 1100mM - 1300mM i.e. about 30-50% more than the chloride concentration in the external solution. This difference of maximum 50% in the recorded chloride levels is attributed to the fact that the sensors “read” the average amount of free chloride at the interface sensor/cement paste, while the destructively measured water soluble chloride reflects the average free (with possible contribution of physically bound chloride) in the total volume of analyzed cement paste. It can be concluded that for the conditions of this experiment, more reliable free chloride content is measured via the sensors’ readings. Hence, if chloride thresholds for corrosion initiation are to be determined, the sensors’ readings will be more representative and accurate if compared to destructive water soluble chloride determination.

Concrete structures exposed to aggressive aqueous media (waste water, soft water, fresh water, ground water, sea water, agricultural or agro-industrial environments), due to their porous nature, are susceptible to a variety of degradation processes resulting from the ingress and/or presence of water. In addition to chemical and physical degradation processes, the presence of water contributes to undesirable changes in the material properties resulting from the activities of living organisms, i.e. biodeterioration. Since microorganisms are ubiquitous in almost every habitat and possess an amazingly diversified metabolic versatility, their presence on building materials is quite normal often, they can infer deterioration that can be detrimental (loss of alkalinity, erosion, spalling of the concrete skin, corrosion of rebar’s, loss of water- or air tightness…). The deleterious effect of microorganisms, mainly bacteria and fungi, on the cementitious matrix has been found to be linked, on the one hand, with the production of aggressive metabolites (acids, CO2, sulfur compounds, etc.) but also, on the other hand, with some specific, physical and chemical effects of the microorganisms themselves through the formation of biofilm on the surface. Moreover, the intrinsic properties of the cementitious matrix (porosity, roughness, mineralogical and/or chemical composition) can also influence the biofilm characteristics, but these phenomena have not been understood thoroughly as of yet. Nonetheless, a serious review about understanding interactions between cementitious materials and microorganisms has been reported [1].

These deteriorations lead to a significant increase in the cost of repairing structures and to loss of production income, but may also lead to pollution issues resulting, for example, from waste water leakage to the environment. Also, building facades, and notably concrete external walls, can be affected by biological stains, which alter aesthetical quality of the construction, sometimes very quickly, and lead to significant cleaning costs. Microorganisms, mainly algae, responsible for these alterations have been quite well identified. Research is now rather focused on determining colonization mechanisms, and notably influencing material-related factors, and on development of preventive or curative, and preferentially environmentally friendly, solutions to protect external walls. However, up to now, no clear results about the efficiency of these various protection solutions are available.

Stray current arising from direct current electrified traction systems and then circulating in reinforced concrete near railways is known to induce corrosion on embedded steel reinforcement. The present paper will review the principles of stray current induced corrosion in reinforced concrete, which is relatively uncommon but with significant impact in practice.

Within one of the approaches to ease this kind of specific corrosion in reinforced concrete, carbon fibres (CF) can be added to enhance the conductivity of concrete, subsequently reduce the stray current density and/or direct the stray current dissipation in a desired manner. The side effects (such as increasing the bulk matrix porosity) caused by CF, which can in turn reduce the general corrosion resistance of reinforced concrete, will be compensated by adding silica fume (SF). The combination of CF and SF can be a potentially feasible and original application to reduce the risk of stray current induced corrosion in reinforced concrete, without obvious negative side effects.