The key question for “ASR performance testing” when subjecting aggregates containing alkalis-and during service life possibly releasing alkalis (“ARA aggregates”)-is whether such properties will be accounted for during the performance testing. Further, how should test results from a testing method assessing the potential alkali contribution from an aggregate (e.g. RILEM AAR-8) be interpreted in context of performance testing and in lab/field relation of such tests? To investigate this, an attempt is made to detect the alkali release as well as the change of expansion when subjecting ARA aggregates to RILEM AAR-10 testing (and AAR-8). The “ARA-proof-of-concept” in concrete expansion testing is demonstrated (preliminary results) in the present study by including “non-ASR-reactive” alkali releasing fine aggregate to a medium reactive concrete mix design. Further, because the alkali release expectedly is more pronounced in the fine fraction including filler, the attempt is made to explicitly address the effect of filler content and properties on the release. The testing methods used in the study include RILEM AAR-10, RILEM AAR-8 (on “bulk” 0/4 mm and – modified – on individual fractions with and without filler) and high-pressure pore water extraction. The background context, program outline and preliminary results are presented. The preliminary results support the hypothesis that a significant part of “ARA” is accounted for during the concrete prism testing, but this should be validated also for other aggregates. The work is still ongoing, and studies on granulometric effects arealsoinprogress.

The project investigates several correlations between properties measured on cement pastes (heat of hydration, bound water, porosity) and mortars (compressive strength). Correlations are powerful tools in material evaluation, when trends noted for one property can be extrapolated to predict another property. This is particularly interesting nowadays, when many new binders are introduced to replace cement and reduce the CO2 release due to concrete. The effect of temperature on hydration, phase assemblages, porosity, and compressive strength of different composite binders, mainly ternary blends, with high replacement was studied at 8, 20, and 38 °C. The properties of blended systems with 45 and 55% replacements can be comparable to the neat Portland cement system at late age (>91 days) when cured at ≤ 20 °C. Increasing temperature accelerates the reaction of supplementary cementitious materials (SCMs), resulting in reducing the difference in the properties between the blended system and the plain system at early age. Property development at high temperatures slows down faster than the low temperatures. On the contrary, blended systems show poor reactivities at low temperatures, particularly at early age. The influence of temperature on phase assemblages is mainly for AFm and AFt, in which monosulfate and AFm containing SO3-CO3-OH are formed at high temperatures and poorly crystalline AFm is formed at low temperatures.

The relationships between different measured characterizations were observed. A very good linear relationship between heat of hydration and compressive strength was found at all temperatures which can be used to predict the compressive strength up to 7 days, but higher uncertainty at late age. A correlation between bound water and compressive strength is also good but one needs to be cautious at late age and high temperature. The MIP total porosity follows globally the same trend as compressive strength, while the capillary porosity cannot explain the development of compressive strength. Bound water/heat of hydration, MIP total porosity/heat of hydration, and bound water/MIP total porosity also present a good linear relationship between hydration and microstructure.

Kompositbindemedel med hög andel SCM i svenskt klimat: temperaturens inverkan på mikrostruktur och beständighet

Projektet undersöker flera samband mellan egenskaper framtagna på cementpastor (hydratiseringsvärme, bundet vatten, porositet) och murbruk (tryckhållfasthet). Korrelationer är kraftfulla verktyg i materialutvärdering, när trender noterade för en egenskap kan extrapoleras för att förutsäga en annan egenskap. Detta är särskilt intressant nuförtiden, när många nya bindemedel introduceras för att ersätta cement och minska koldioxidutsläppet från betong. Effekten av temperatur på hydratisering, fassammansättningar, porositet och tryckhållfasthet hos olika kompositbindemedel, huvudsakligen ternära blandningar, med hög ersättning studerades vid 8, 20 och 38 °C. Egenskaperna hos blandade system med 45 och 55 % ersättningar kan vara jämförbara med det rena Portlandcementsystemet vid sen ålder (>91 dagar) när det härdas vid ≤ 20 °C. Ökande temperatur påskyndar reaktionen av alternativa bindemedel, vilket resulterar i att skillnaden i egenskaperna mellan det blandade systemet och det vanliga systemet vid tidig ålder minskar. Fastighetsutveckling vid höga temperaturer minskar snabbare än de låga temperaturerna. Tvärtom uppvisar blandade system dåliga reaktiviteter vid låga temperaturer, särskilt i tidig ålder. Temperaturens inverkan på fassammansättningar är främst för AFm och AFt, där monosulfat och AFm innehållande SO3-CO3-OH bildas vid höga temperaturer och dåligt kristallint AFm bildas vid låga temperaturer.

Sambanden mellan olika uppmätta egenskaper observerades. Ett mycket bra linjärt samband mellan hydreringsvärme och tryckhållfasthet konstaterades vid alla temperaturer som kan användas för att förutsäga tryckhållfastheten upp till 7 dagar, men högre osäkerhet vid sen ålder. En korrelation mellan bundet vatten och tryckhållfasthet är också bra men avskiljer sig vid sen ålder och hög temperatur. Den totala MIP-porositeten följer generellt samma trend som tryckhållfasthet, medan kapillärporositeten inte kan användas för att förutse utvecklingen av tryckhållfasthet. Bundet vatten/hydratiseringsvärme, MIP total porositet/hydratiseringsvärme och bundet vatten/MIP total porositet uppvisar också ett bra linjärt förhållande mellan hydratisering och mikrostruktur.

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.

The report presents an investigation of the role of the sulfate balance in blended binders with slag (ground granulated blast furnace type, GGBS) or fly ash (low calcium type) in achieving improved sulfate resistance (SR) when using non-SR CEM I. The investigation involved experiments with sulfate-doped vs. undoped blended binders, pastes and mortars with and without exposure to sulfate attack, which was induced by immersion in Na2SO4 solution using a laboratory method. The results reveal the benefit of a sulfate level adjustment to promote improved behaviour during sulfate attack: doped blends yielded lower expansion during sulfate attack and reduced internal damage compared to undoped alternatives. Sulfate-doping increased the potential of slag and fly ash to mitigate sulfate attack with non-SR cement.

The Swedish construction industry is generating a save and affordable built environment for transport, work and living but it is faced with a huge challenge: drastic reduction of greenhouse gases and an increase of circularity in their production cycles. One material, which has inherently embodied CO2, is limestone, which is needed for the production of Portland cement, the essential ingredient in concrete. The CO2 emission during cement production can be drastically compensated by so called supplementary cementitious materials (SCM), which replace cement components causing CO2 emissions. SCM can be used by incorporating them into Portland cement or can be used directly by mixing into concrete. However, traditionally used SCM such as ground granulated blast furnace slag or fly ash are only available in limited amounts in Sweden, not matching the domestic cement production. An alternative to those more traditional SCM is activated or calcined clay, which reacts similar to blast furnace slag or fly ash. Calcined clay is created from natural clays by heating up to 700 ° - 800 °C, where it become very reactive. In this roadmap the state-of-the-art about activated clays is shown from a Swedish perspective. It also shows challenges and needs that have been formulated for a future implementation of activated clays as a component of low carbon concrete.