Biomass ash as supplementary cementitious materials: Characterization, application, and re-conditioning New types of supplementary cementitious materials (SCM) are in demand, due to the foreseen decrease in the availability of traditional SCM (i.e. coal fly ash and ground granulated blast furnace slags). Hence, this project investigated the potential of using biomass ashes as SCM. The studied ashes came from two different sectors, pulp and paper and energy producers, and from different plants in each case. Both fly and bottom ashes were investigated in terms of chemical composition and their evolution in time, mineralogy, reactivity, and participation in the hydration of cementitious binders. The re-conditioning of the ashes was also explored to limit the presence of undesired components, such as Cl and S. The use of blends of biomass ashes of different types and origins was investigated as well. Finally, mortar bars containing ashes in different proportions were cast to check their mechanical properties. The study revealed that the composition and overall properties of ashes did not change significantly in time (i.e. for different sampling dates), but that big differences could be found between different plants (because of differences in the production processes. Chlorine and sulphur could be washed away easily by simple immersion in water, but high alkali contents remained in some cases. Generally, fly ashes tend to be more reactive than bottom ashes, but exceptions were found Some ashes were found to be hydraulic reactive. Most samples exhibited a high LOI, resulting in some cases in high water absorption and poor hydration of the cement, which resulted in poor mechanical properties. The use of blends of ashes led to a reduction of the spread in reactivity and an increase in the average reactivity. The results showed that sufficient compressive strength could be reached in mortars containing biomass ash.

Concrete is the most used material in the world (buildings, infrastructure, transport) and its production is continuously increasing over the years because of the growth of the population, the urbanisation, and the infrastructure development. Unfortunately, the production of the main component of concrete, cement, causes inevitable CO2 emissions, accounting for 6% of the total anthropogenic CO2 emissions. The most efficient way to reduce this environmental footprint is to reduce the clinker factor in cement or to reduce the cement content in concrete, which is done by replacing a part of the cement by Supplementary Cementitious Materials (SCM). However, the most commonly used SCM (fly ash and ground granulated blast furnace slag) are only available in a low amount in Sweden. New SCM must be find.The objective of this project was to evaluate the potential of using Swedish clays as SCM. An inventory of available clays was performed in a first step. Then, as clays need to be activated before use with cement, different activation procedures were tested. A selection of clays was mixed with cement either in binary mixes (cement + activated clay) or in ternary mixes (cement + activated clay + limestone). The hydration properties and the microstructure of binder pastes were investigated, as well as the strength development of mortars. Finally, a life cycle analysis (LCA) was performed to evaluate the positive impact on the CO2 emissions when clays are used as SCM.The results of the project highlighted the good potential of using Swedish clays in concrete to decrease the environmental footprint due to the cement and concrete industries. In particular, the clays can be activated through mechanical and thermal treatment, depending on the type of clay. Thermal treatment in temperature ranges between 600-800 degrees is preferred for sedimentary clays, while a mechanical treatment by ball milling gives better results with marine clays. A satisfactory strength is achieved in mortar samples cast with calcined clays. This was achieved by replacing the cement with 30% of calcined clay and 15% of limestone. Finally, the LCA calculation shows that the use of clay in a ternary binder lead to a reduction of approx. 34% of the CO2 emissions.

This report describes results of an investigation on the sulfate resistance of dual blended binder of mortar and concrete specimens over a period of 1 year. The focus is on showing the importance of the chemistry of the components when discussing sulfate resistance and the relation of that to the hydrate phase assemblage. Moreover the importance of the test method for evaluations is pointed out.

The report summarizes a state-of-the-art for sprayed concrete applied for ground support in tunnel environments, in Sweden and several European countries, with focus on the components, the mix design and the guidelines and specifications. It focuses also on the addition of supplementary cementitious materials (SCM), where the use, the common practice and the long-term experience vary from country to country. The report presents numerous examples of applications in Sweden and seven other European countries. It also gives an overview about the possible exposure risks and summarizes the relevant durability issues. Along with specifications in international standards and guidelines it also reviews the national requirements in Sweden, Norway, Finland, Austria, France, Germany and Switzerland.

This report describes a study on the effects of ground granulated blast furnace slag, low calcium fly ash and metakaolin on the hydration behavior of different binder pastes blended with these SCM. The study investigated early heat development, phase assemblages at different ages, strength gain, changes in porosity and pore sizes, pore water OH-concentration, development of the microstructure and the micro chemistry of the binder pastes.It was shown that all SCM impact the pore size distribution of pastes of different ages. Compared to a reference paste without SCM, SCM containing pastes shift their pore size range to smaller sizes, the more SCM the pastes contain. The total porosity depends on the type of SCM. With slag, there was a tendency to decrease the total porosity with increasing SCM content. With fly ash, total porosity was increased with increasing fly ash content. The strength development of slag and fly ash containing mortars is under that of a Portland cement reference mortar within the first 28 days. However, after 28 d strength gain, in particular with fly ash is considerable compared to the reference. With metakaolin already at early ages a strong increase in strength was observed. After that, the strength development was parallel the one of the reference mortar. Aluminum containing SCM contribute to the formation of AFm phases. AFm phases increase the chloride binding in seawater or deicing salt exposed concretes. In particular metakaolin and fly ash contribute, due to their high alumina content, to the formation of AFm phases but also increase the aluminum content in the C-S-H phases.

Rapporten beskriver en studie om inverkan av tillsatsmaterial (SCM) som mald granulerad masugnslagg, kiselhaltig flygaska och metakaolin på hydratationsförloppet hos cementpastor med sammansatta bindemedel, dvs en blandning av cement och en av dessa SCM.Studien undersökte den tidiga värmeutvecklingen, vilka cementhydratfaser som utvecklas vid olika ålder, hållfasthetsutvecklingen, förändringarna i porositet och porstorlekar, porvattnets OH-koncentration och utvecklingen av mikrostruktur och mikrokemi i cementpastan, beroende bindemedlets sammansättning.Studien visar att samtliga tillsatsmaterial (SCM) påverkar porstorleksfördelningen i cementpastan. Jämfört med en referenspasta med enbart cement, sker i cementpastor med blandcement (cement plus SCM) en ändring mot finare porstorlekar, dvs mindre pordiameter, ju högre andelen SCM i blandningen är. Den totala porositeten beror på vilken typ av SCM som används i blandningen. Slagg visade tendensen att leda till minskad total porositet med ökande slagghalt. Med flygaska ökade däremot den totala porositeten med ökande halt flygaska.Hållfastheten som utvecklas hos bruk med bindemedel med slagg och flygaska är lägre än den hos referensbruk med enbart Portland cement, under de första 28 dygnen. Efter 28 dygn märks däremot en mer markant hållfasthetsutveckling jämfört med referensbruket, i synnerhet hos bruk med flygaska. Med metakaolin noterades en markant ökning av hållfastheten redan under de första dygnen, men hållfasthetsutvecklingen fortsatte därefter i samma takt som (parallellt med) referensbruket.Aluminiumhaltiga SCM leder vid hydratation till bildning av hydratfaser av typen AFm.AFm-faser bidrar till ökad kloridbindning i cementpastan, en fördel för betong som utsätts för t ex havsvatten eller avisningssalter på vintervägar. I synnerhet metakaolin och flygaska, tack vare den höga aluminiumhalten, leder till cementhydrater av typen AFm, samtidigt som de även ökar aluminiumhalten i kalciumsilikathydraten (C-S-H-faser).

To facilitate the long term durability predictions of nuclear waste repositories, acceleration methods enhancing calcium leaching process from cementitious materials are needed, even though mechanisms not necessarily comparable to those predominant in a natural leaching process may be developed. In the previously published acceleration methods the samples are very small, which limits further physical or mechanical tests. In this paper, a new acceleration method based on electro-chemical migration is presented. The method although not driven with the same kinetics as in natural leaching, was designed in such a way that unnecessarily destructive by-effects could be minimized while promoting a higher leaching rate for a sample size suitable for further testing the mechanical and physical properties. It is shown that approximately 1 × 106C of electrical charge per paste specimen of size Ø50 × 75 mm (approximately 230 g) is required to leach out the total amount of Portlandite. The chemical and mineralogical properties of leached samples are characterized by various techniques. It is concluded that aged samples are comparable to those leached in a natural leaching process as both are characterized by a layered system comprising an unaltered core delineated by total dissolution of Portlandite followed by a progressive decalcification of the calcium silicate hydrate gel.