Low Carbon Concrete Possibilities: EPD and Regulations in Northern Periphery and Arctic

Concrete is one of the most common building materials in the Northern Periphery and Arctic, and therefore we should pay attention to its quality while reducing its carbon footprint. The concrete industry has established many measures to limit greenhouse gas emissions from concrete, as stated in the environmental product declaration (EPD). The most significant contributor is cement (common dose between 250 and 600 kg per 1 m3 of concrete) in a concrete binder. Aside from the use of alternative fuels for cement production, new alternative materials for cement replacement are being sought. Those materials are called supplementary cementitious materials and mainly originate from industrial waste streams. Some of the materials are already standard and limited by the maximum allowed replacement, and some are new and still under investigation. The benefits and limitations of low-carbon concrete regulations in Norway, Sweden, Iceland, and Finland are demonstrated on three different concrete mixes in this article. The sorting of a reference mix and two low-carbon concrete mixes according to 4 different systems showed the informative character of the Icelandic system and the underestimation of possibilities for the carbon footprint of concrete in the Swedish classification system

Large-scale shear test of brash ice

A large-scale shear apparatus has been originally developed and built to test the mechanical properties of coarsegrained material. It was used to evaluate the shear behaviour of brash ice. The brash ice blocks were collected at Luleå harbour in two separate measuring campaigns in March 2020 and March 2021. The shear cylinder was loaded with brash ice in Luleå port in two different locations for the two test campaigns, and the displacementcontrolled shear tests were conducted. A vertical actuator was used to set a constant normal load and then a horizontal actuator was used to move the shear swing. In this setup, time, forces, and displacements were recorded at the forward and return stroke of the horizontal actuator. In total 6 shear cycles on two brash ice samples with axial stress of 4.8 kPa, 2 kPa and 1 kPa were performed. The test data was analysed to determine the relationship between shear stress and shear strain. The macro-porosity and confining axial force were found to be the most influential factors in determining the strength and deformation of the brash ice. Furthermore, an attempt has been made to estimate a few parameters of a material model known as the Continuous Surface Cap Model.publishedVersio

Effect of Carbon Nanotube Aqueous Dispersion Quality on Mechanical Properties of Cement Composite

An effect of the quality of carbon nanotube (CNT) dispersions added to cement on paste mechanical properties has been studied. High-quality dispersions of few-walled CNT (FWCNTs) were produced in two steps. First, FWCNTs were functionalized in a mixture of nitric and sulfuric acids (70 wt.% and 96 wt.%, resp.) at 80 ∘C . Second, functionalized FWCNTs were washed out by acetone to remove carboxylated carbonaceous fragments (CCFs) formed during CNT oxidation. Mechanical test results showed 2-fold increase in the compressive strength of the cement paste prepared from the dispersion of acetone-washed functionalized FWCNTs, which is believed to occur due to the chemical interaction between cement matrix and functional groups (–COOH and –OH). Utilisation of unwashed FWCNTs led to a marginal improvement of mechanical properties of the cement pastes, whereas surfactant-treated functionalized FWCNT dispersions only worsened the mechanical properties.Peer reviewe

Synthesis of Carbon Nanotubes and Nanofibers on Silica and Cement Matrix Materials

In order to create strong composite materials, a good dispersion of carbon nanotubes (CNTs) and nanofibers (CNFs) in a matrix material must be obtained. We proposed a simple method of growing the desirable carbon nanomaterial directly on the surface of matrix particles. CNTs and CNFs were synthesised on the surface of model object, silica fume particles impregnated by iron salt, and directly on pristine cement particles, naturally containing iron oxide. Acetylene was successfully utilised as a carbon source in the temperature range from 550 to 750 C. 5–10 walled CNTs with diameters of 10–15 nm at 600 C and 12–20 nm at 750 C were synthesised on silica particles. In case of cement particles, mainly CNFs with a diameter of around 30 nm were grown. It was shown that high temperatures caused chemical and physical transformation of cement particles.Peer reviewe

A novel cement-based hybrid material

Carbon nanotubes (CNTs) and carbon nanofibers (CNFs) are known to possess exceptional tensile strength, elastic modulus and electrical and thermal conductivity. They are promising candidates for the next-generation high-performance structural and multi-functional composite materials. However, one of the largest obstacles to creating strong, electrically or thermally conductive CNT/CNF composites is the difficulty of getting a good dispersion of the carbon nanomaterials in a matrix. Typically, time-consuming steps of purification and functionalization of the carbon nanomaterial are required. We propose a new approach to grow CNTs/CNFs directly on the surface of matrix particles. As the matrix we selected cement, the most important construction material. We synthesized in a simple one-step process a novel cement hybrid material (CHM), wherein CNTs and CNFs are attached to the cement particles. The CHM has been proven to increase 2 times the compressive strength and 40 times the electrical conductivity of the hardened paste, i.e. concrete without sand.Peer reviewe

Robotized formless concreting – (RoboBet) – pilot project

"RoboBet" var ett högriskprojekt för genomförbarhet i syfte att validera en ny metod för 3D-tryckning av betong. Konceptet är baserat på en större kontroll av härdningsprocesser via kombination av skräddarsydda kapslar som innehåller accelererande ämnen och ytterligare behandlingar som möjliggör frisättning av dessa ämnen på begäran under tryckningen. Projektet testades flera typer av accelererande föreningar. De producerade kapslarna blandades med färska cement pasta och sprickandes därefter genom applicering av ultraljud. Det frisatta materialet påskyndade hydreringsprocessen och förkortade den initiala inställningen i vissa fall. De erhållna resultaten bekräftade generellt konceptets giltighet men de använda inkapslingsprocesserna sänkte acceleratorernas effektivitet avsevärt. Mer grundläggande forskning med fokus på optimering av inkapslingsprocesserna måste utföras innan det faktiska systemet kan vidareutvecklas och så småningom uppskalas.RoboBet Robotiserad formlös beton

Optimization of the Process Parameters Controlling the Degree of Amorphization during Mechanical Activation of Clay Using the Taguchi Method

Mechanical activation in a planetary ball mill (BM) is an environmentally friendly process able to enhance the chemical and pozzolanic activity of natural clays. Those materials can be used as supplementary cementitious materials (SCMs) to partially replace Portland cement in concrete. The process parameters of the BM are directly related to the degree of amorphization and thus to the enhancement of the chemical activity. Design of experiments (DOE) is a well-known statistical tool, which can assist in selecting optimized conditions and in obtaining systematic data. However, full factorial design requires a large number of experiment. Taguchi method is based on the use of an Orthogonal Array (OA) to evaluate optimization of the selected factors but with less required experiments. In this study, three factors, each on 2 levels, were selected: ball to powder ratio (B/P) with level 3 and 25, time of grinding with level 5 and 20, and water to powder ratio (W/P) with level 0 and 1. The degree of amorphization (DOA) was selected as the main response for the Taguchi method. DOA was calculated as the ratio between the integral intensities of the main peak of the kaolinite [001] before and after grinding. For dry grinding, the predicted optimized value of DOA complied with the experimental results. Maximized DOA value was achieved for B/P equal to 25 and the grinding duration of 20. This method can be a valuable tool to predict the amorphization degree of minerals present in the natural clay, leading to the optimization of the mechanical activation process

Bond Strength between Glass Fiber Fabrics and Low Water-to-Binder Ratio Mortar

Full utilization of mechanical properties of glass fiber fabric-reinforced cement composites is very limited due to a low bond strength between fibers and the binder matrix. An experimental setup was developed and evaluated to correlate the mortar penetration depth with several key parameters. The studied parameters included fresh mortar properties, compressive and flexural strengths of mortar, the fabric/mortar bond strength, fabric pullout strength, and a single-lap shear strength. Results showed that an average penetration of mortar did not exceed 100 mu m even at a higher water-to-binder ratio. The maximum particle size of the used fillers should be below an average spacing of single glass fibers, which in this case was less than 20 mu m to avoid the sieving effect, preventing effective penetration. The pullout strength was strongly affected by the penetration depth, while the single-lap shear strength was also additionally affected by the mechanical properties of the mortar.Peer reviewe

Effects of fineness and chemical composition of blast furnace slag on properties of alkali-activated binder

Abstract: The effects of fines and chemical composition of three types of ground granulated blast furnace slag (GGBFS) on various concrete properties were studied. Those studied were alkali activated by liquid sodium silicate (SS) and sodium carbonate (SC). Flowability, setting times, compressive strength, efflorescence, and carbonation resistance and shrinkage were tested. The chemical composition and microstructure of the solidified matrixes were studied by X-ray diffraction (XRD), thermogravimetric analysis (TGA) and scanning electron microscopy (SEM) coupled with EDX analyser. The results showed that the particle size distribution of the slags and the activator type had significantly stronger effects on all measured properties than their chemical composition. The highest compressive strength values were obtained for the finest slag, which having also the lowest MgO content. SC-activated mortar produced nearly the same compressive strength values independently of the used slag. The most intensive efflorescence and the lowest carbonation resistance developed on mortars based on slag containing 12% of MgO and the lowest fineness. The slag with the highest specific surface area and the lowest MgO content developed a homogenous microstructure, highest reaction temperature and lowest drying shrinkage. Thermogravimetric analysis indicated the presence of C-(A)-S-H, hydrotalcite HT, and carbonate like-phases in all studied mortars.Validerad;2019;Nivå 2;2019-10-28 (johcin)</p