Environmentally Friendly Pervious Concrete for Treating Deicer-Laden Stormwater: Phase II

In Phase I of this project, graphene oxide (GO)-modified pervious concrete was developed using coal fly ash as the sole binder. The primary objectives of Phase II of this project were (1) to evaluate the stormwater infiltration capacity of GO-modified fly ash pervious concrete; (2) to evaluate the durability performance of GO-modified fly ash pervious concrete using freeze/thaw and salt resistance testing methods; and (3) to use advanced analytical tools to fully characterize the GO-modified fly ash binder. Test results indicate different degrees of reduction in concentrations of possible pollutants in stormwater—copper, zinc, sulphate, chloride, ammonia, nitrate, and total phosphate. The incorporation of GO significantly improved the resistance of pervious concrete to freeze/thaw cycles and ambient-temperature salt attack. The specimens were examined using X-ray diffraction, which revealed that the mineralogy and the chemical composition of fly ash pastes differ considerably from those of cement pastes. Nuclear magnetic resonance was used to study the chemical structure and ordering of different hydrates, and provided enhanced understanding of the freeze/thaw and salt scaling resistance of fly ash pervious concrete and the role of GO

The Deleterious Chemical Effects of Concentrated Deicing Solutions on Portland Cement Concrete, Literature Review, TR-480, 2008

This research project investigated the effects of concentrated brines of magnesium chloride, calcium chloride, sodium chloride, and calcium magnesium acetate on portland cement concrete. Although known to be effective at deicing and anti-icing, the deleterious effects these chemicals may have on concrete have not been well documented. As a result of this research, it was determined that there is significant evidence that magnesium chloride and calcium chloride chemically interact with hardened portland cement paste in concrete resulting in expansive cracking, increased permeability, and a significant loss in compressive strength. Although the same effects were not seen with sodium chloride brines, it was shown that sodium chloride brines have the highest rate of ingress into hardened concrete. This latter fact is significant with respect to corrosion of embedded steel. The mechanism for attack of hardened cement paste varies with deicer chemical but in general, a chemical reaction between chlorides and cement hydration products results in the dissolution of the hardened cement paste and formation of oxychloride phases, which are expansive. The chemical attack of the hardened cement paste is significantly reduced if supplementary cementitious materials are included in the concrete mixture. Both coal fly ash and ground granulated blast furnace slag were found to be effective at mitigating the chemical attack caused by the deicers tested. In the tests performed, ground granulated blast furnace slag performed better as a mitigation strategy as compared to coal fly ash. Additionally, siloxane and silane sealants were effective at slowing the ingress of deicing chemicals into the concrete and thereby reducing the observed distress. In general, the siloxane sealant appeared to be more effective than the silane, but both were effective and should be considered as a maintenance strategy

Rietveld Quantitative Phase Analysis of OPC Clinkers, Cements and Hydration Products

Universidad de Málaga. Campus de Excelencia Interacional. Andalucía Tech

Impact of carbonation on unsaturated water transport properties of cement-based materials

International audienceIn unsaturated conditions, the durability of concrete structures is strongly dependent on the evolution of the amount of free water within concrete porosity. Reliable durability assessment of concrete structures in relation to their environment thus requires accurate unsaturated water transport description as well as reliable input data. The effect of carbonation on water transport remains poorly studied and data are lacking. It was then the purpose of this article to acquire all the data needed to describe unsaturated water transport in carbonated cementitious materials (porosity, water retention and unsaturated permeability). Four hardened pastes made with four different binders were carbonated at 3% CO2 to ensure representativeness with natural carbonation. Beyond the modification of the water retention curve and porosity clogging, significant microcracking due to carbonation shrinkage was observed. The consequence on permeability highlighted a competition between porosity clogging and microcracking that was dependent on the initial mineralogical composition

Biodeterioration of cementitious materials in biogas digester

In biogas production plants, concrete structures suffer chemical and biological attacks during the anaerobic digestion process. The attack on concrete may be linked to the effects of (i) organic acids; (ii) ammonium and CO2 co-produced by the microorganisms’ metabolisms; and (iii) the bacteria’s ability to form biofilms on the concrete surface. In a context of biogas industry expansion, the mechanisms of concrete deterioration need to be better understood in order to propose innovative, efficient solutions. This study aims, firstly, to characterise the evolution of the biochemical composition of the biodegradable wastes during digestion so as to identify the compounds that are aggressive for concrete. Secondly, it aims to evaluate the mechanisms of concrete deterioration in anaerobic digesters. CEM I paste specimens were immersed in synthetic inoculated biowaste in anaerobic digestion conditions. The liquid fractions were analysed chemically. The alteration mechanisms of the cementitious matrices were investigated using XRD and SEM analyses. The maximal total concentration of organic acids was 65 mmol/L in the liquid fraction during the digestion process. The pH evolution showed two phases: acidification in the first few days and then a slow increase to pH 7–8. In only 4 weeks, an abundant biofilm developed on the cement paste surface. Biodeterioration leads to calcium leaching and carbonation of the cement past

Influence of supplementary cementitious materials on hydration, microstructure development, and durability of concrete

In recent years the use of supplementary cementitious materials in the production of concrete has become an ever more frequent trend, since such use contributes to a sustainable concrete industry. The main reason for this lies in the reduction of the specific energy requirement and of carbon dioxide emissions in the production of cement (OPC). One such environmentally friendly product is fly ash (FA), which occurs as a by-product of coal-fired thermal power plants. In the first part of the thesis the hydration of OPC and FA at early ages, as well as at later ages, was monitored by means of calorimetry and thermogravimetry. During the first hours the FA retarded the hydration of OPC, particularly the belite hydration. Up to an age of 28 days, the FA exerted a physical nucleation effect on the OPC hydration, which did not compensate for the dilution effect. Furthermore, between 21 and 28 days, a decrease was observed in the amount of calcium hydroxide (CH), and a corresponding increase in the amount of bound water relative to the OPC content, due to a pozzolanic reaction, indicating a change in the hydration products that are formed in the FA blended cement, i.e. less CH and more C-S-H and AFm phases relative to the OPC content. Comparing the two investigated types of FA, siliceous and calcareous FA, no clear difference can be observed with regard to the decrease in the amount of CH. On the other hand, the amount of hydrated products increased significantly up to 28 days, and then not changed much up to one year in the case of the cement paste with siliceous FA. In contrast, in cement paste made by using calcareous FA, the amount of hydrated products increased gradually up to one year. Over a period of one year the consumption of CH was 50% greater in the case of cement pastes containing 30% FA than in the case of cement paste without such an addition. This phenomenon was reflected over time in the observed increase in the mechanical strength of the binder. After 90 days, the compressive strength of concrete in which 20% of the OPC was replaced by FA exceeded the compressive strength of the unmodified concrete. Furthermore, when the replacement level was 50%, the 90 day compressive strengths were almost comparable. When characterizing the mechanical properties of two concrete mixtures made with different types of carbonate aggregate but with identical mix designs, it was found that, in the case of concrete made by using dolostone aggregate, there was a considerable increase in the compressive strength (24%) and modulus of elasticity (13%), compared with the values which corresponded to concrete made by using limestone aggregate. These differences initiated a further investigation into the alkali-carbonate reaction (ACR) which occurs when carbonate minerals react in an alkaline environment. The first process of the mechanisms of ACR is called dedolomitization. In contrast to statements which can be found in the literature, in the case of the used high-purity dolostone aggregate, which did not contain any reactive silica, the dedolomitization was observed after a 6-month exposure period in water. That means that no accelerators in the form of highly alkaline solutions or reactive components are needed to initiate the reaction. Moreover, a new phase which was rich in Si, Al and Mg atoms, was observed between the dedolomitizated aggregate and the secondary calcite. It is supposed that this phenomenon may be responsible for the improvement in the mechanical characteristics of the concrete made by using dolostone aggregate, due to the denser interfacial transition zone and better interlocking of the cement binder and the aggregate grains. The behaviour of the FA modified concrete in aggressive environments was also investigated, and compared to that of unmodified concrete. The study of chloride ingress showed that the FA modified concretes achieved smaller penetration depths, and thus required smaller cover depths. The test results indicated a beneficial effect of FA modified concrete, even when 50% of the OPC was replaced by FA. The results correspond well with measured porosity by means of mercury porosimetry. A higher percentage of ink-bottle porosity was confirmed experimentally in the case of the FA modified concrete. This leads to a lower effective porosity, which means that a higher resistance of the concrete to chloride penetration was achieved. Not only the porosity but also the chemical composition of the FA plays an important role in chloride diffusion in concrete. The concrete with siliceous FA, which had a lower content of calcium, showed better resistance to chloride penetration up to 90 days than the concrete with calcareous FA. On the other hand, after 126 days the concrete with -vicalcareous FA showed better chloride resistance characteristics than the concrete with siliceous FA. This phenomenon seemed to correlate with experimentally observed compressive strength results. The chloride binding was also tested by means of the differences between the amount of water and total-soluble chloride content. The effect of the replacement of OPC by FA on chloride binding capacity was not particularly pronounced. However, the assumption that FA blended cements containing higher amounts of AFm phases relative to the OPC content, which are favourable for chloride binding, was confirmed by calorimetry. The performance of FA modified concrete was poorer in the case of carbonation and frost/salt attack by de-icing salts. With regard to carbonation, the carbonation depth increased with increasing FA content in the concrete mixture that was exposed for 18 weeks to a 10 vol% CO2 environment. Nevertheless, the depth of carbonation at the end of the FA modified concrete’s life could still be acceptable in normal environments in the cases when 20% of the OPC is replaced by FA. In the case of concrete structures that are exposed to the combined action of frost and de-icing salts, the addition of FA should not be greater than 20%. Although FA modified concrete mixtures can achieve a high compressive strength class, the concrete mixture containing 50% of FA proved to have poorer resistance to frost/salt attack. Also the impact of the type of chloride salts on frost/salt scaling was discussed. The test results indicated that sodium, magnesium, and calcium chloride at solution concentrations of 3% showed no significant differences of the unmodified concrete mixture. Otherwise, more rapid scaling rate was observed in the case when the solution concentration of CaCl2 was increased to 24%

The use of municipal solid waste incineration ash in various building materials : a Belgian point of view

Huge amounts of waste are being generated, and even though the incineration process reduces the mass and volume of waste to a large extent, massive amounts of residues still remain. On average, out of 1.3 billion tons of municipal solid wastes generated per year, around 130 and 2.1 million tons are incinerated in the world and in Belgium, respectively. Around 400 kT of bottom ash residues are generated in Flanders, out of which only 102 kT are utilized here, and the rest is exported or landfilled due to non-conformity to environmental regulations. Landfilling makes the valuable resources in the residues unavailable and results in more primary raw materials being used, increasing mining and related hazards. Identifying and employing the right pre-treatment technique for the highest value application is the key to attaining a circular economy. We reviewed the present pre-treatment and utilization scenarios in Belgium, and the advancements in research around the world for realization of maximum utilization are reported in this paper. Uses of the material in the cement industry as a binder and cement raw meal replacement are identified as possible effective utilization options for large quantities of bottom ash. Pre-treatment techniques that could facilitate this use are also discussed. With all the research evidence available, there is now a need for combined efforts from incineration and the cement industry for technical and economic optimization of the process flow

Deterioration mechanisms and durability of sprayed concrete for rock support in tunnels

This thesis deals with deterioration mechanisms affecting steel fibre reinforced sprayed concrete used for rock support in tunnels. Physical and chemical degradation of sprayed concrete linings may contribute to destabilisation of the rock mass, involving increased maintenance costs, reduced service life, and a potential safety risk. The principal aims of this work were to a) provide an updated and modern diagnosis of chemical degradation phenomena occurring in steel fibre reinforced concrete used for rock support, b) investigate the reaction mechanisms involved including the possible interaction of different reaction schemes, c) characterise the environmental loads, mainly with respect to water chemistry, microbial activity and hydrogeology, and d) attempt to establish links between scientific findings and practical engineering issues, such as durability and life time aspects, maintenance/repair and consequences for rules and recommendations.Statens vegvesen Vegdirektorate