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Although several studies report the CO2 reduction obtained from alkali-activated materials/geopolymers, only a few investigate their engineering, environmental and economic aspects. The present paper provides an evaluation approach to address these three major aspects of geopolymer concrete by choosing three scenarios for industrial precast applications. Using the analytical hierarchy process, a single sustainability score was determined for three scenarios using technical, environmental and economic parameters. Such sustainability sensitivity analysis led to decision-making for various scenarios. This case study provides an example of reaching these parameters for choosing suitable concrete mixtures for a given application or requirements. The technical and environmental results showed that a wide range of late and early age compressive strength could be achieved by changing the mix composition and proportions. However, all the geopolymer concrete samples exhibited a lower environmental footprint than OPC concrete.

Sensible thermal energy storage using concrete as a storage medium is a promising technology that helps minimize energy in power plant. The purpose of this study is to evaluate the potential benefits of metakaolin (MK) as a partial substitute for fly ash-based geopolymer for heat resistance. As a partial substitute (5 and 20 wt.%) for fly ash (FA), nine metakaolins containing different alumina contents were selected. In order to assess their potential for storing high-temperature thermal energy, physical and microstructural analyses were performed before and after heat exposure up to 500 °C. Low packing density limits the workability of some metakaolins and increases water demand in pastes. The mechanical properties of geopolymer weaken as the temperature is raised (Article Highlights Fly ash was the main precursor of as prepared alkali-activated binders. Adding metakaolin enhances the resistance of hardened materials under thermal load. The higher the alumina content inside metakaolin is, the higher the performance is.

Bitumen is a complex mixture consisting of different hydrocarbons, which can be categorised into substance classes called SARA (saturates, aromatics, resins and asphaltenes) fractions. The saturates, aromatics and resins are further referred to as maltenes or maltene phase. To determine the SARA fractions the asphaltenes were separated from the maltenes in a first step. A standard method to further separate the maltenes is column chromatography (CC). Since column chromatography is a time-consuming and solvent-intensive process, an alternative method for separating maltenes using solid-phase extraction (SPE) was investigated. A total of nine bitumen samples of the same type in different ageing states but from different manufacturers were separated with both methods to determine the mass percentages of the fractions for investigating their comparability. The results show that both methods led to different mass percentages of the fractions. However, with the SPE, separating smaller amounts of maltenes is possible while saving a large amount of material, costs, and workload. Linear regression analyses between the colloidal indices with conventional and rheological parameters revealed that the fractions obtained from SPE led to higher coefficients of determination of the linear regression model. The obtained fractions were further structurally compared with FTIR spectroscopy, whereby the spectra of the SPE fractions and the CC fractions did not show any significant differences. The overall consideration of the results concludes that the SPE can replace the CC.

Alkali-activated binders (AAB) can provide a clean alternative to conventional cement in terms of CO2emissions. However, as yet there are no sufficiently accurate material models to effectively predict the AAB properties, thus making optimal mix design highly costly and reducing the attractiveness of such binders. This work adopts sequential learning (SL) in high-dimensional material spaces (consisting of composition and processing data) to find AABs that exhibit desired properties. The SL approach combines machine learning models and feedback from real experiments. For this purpose, 131 data points were collected from different publications. The data sources are described in detail, and the differences between the binders are discussed. The sought-after target property is the compressive strength of the binders after 28 days. The success is benchmarked in terms of the number of experiments required to find materials with the desired strength. The influence of some constraints was systematically analyzed, e.g., the possibility to parallelize the experiments, the influence of the chosen algorithm and the size of the training data set. The results show the advantage of SL, i.e., the amount of data required can potentially be reduced by at least one order of magnitude compared to traditional machine learning models, while at the same time exploiting highly complex information. This brings applications in laboratory practice within reach.

Crown Copyright © 2022. This study investigates the effects of natural and calcined halloysite clay minerals (“NH” and “CH”, respectively) on the performance of 3D printed alkali-activated materials (AAMs). Halloysite clay minerals are selected as they are low-cost and abundantly available. At first, different characterisation techniques were employed to characterise the NH and CH additives. Mechanical performance, extrusion window, and shape stability of several AAM formulations containing various dosages (0.5 wt% to 5 wt%) of the NH and CH additives were evaluated. The best-performing mixtures in terms of fresh and hardened properties namely, NH-1.5 and CH-1.5 mixtures (containing 1.5 wt% of NH and CH additives, respectively) were then selected for 3D printing. The results showed that the CH-1.5 mixture exhibited enhanced shape stability, buildability, and mechanical properties as compared to the control mixture. The flexural and compressive strengths of 3D printed CH-1.5 samples were 88% and 40%, respectively higher than those of the printed control samples. Using the CH-1.5 mixture, a twisted column with an intricate shape was printed to verify the suitability of the developed CH-modified AAM for the construction of complex structures. This study establishes the use of halloysite clay minerals as low-cost additives for enhancing the mechanical properties and printing performance of AAMs. European Union's Horizon 2020 research and innovation program under the Marie Skłodowska-Curie grant agreement ID: 101029471; National Science Centre, Poland, within Project No. 2020/39/D/ST8/00975 (SONATA-16).

The interfacial transition zone (ITZ) in concrete is known as the weakest link of the material, and significantly affects the properties of concrete. This study aims to investigate the actu...

The rapid increase in waste quantities, as well as the depletion of the natural resources in the near future are some of the major concern worldwide. In response to these problems, as well as to the growing demand for concrete in the construction field, the focus has been directed towards the production of artificial aggregates, as an alternative to natural ones. Artificial aggregates are produced either by sintering or cold bonding method. Compared with the sintering method and besides being an effective recycling solution for a wide variety of wastes and by-product materials, the cold bonding method is characterized by minimal energy consumption, low pollutant emissions and low investment requirements. The use of cold-bonded aggregate as a potential construction material in concrete production is summarized in this manuscript. The paper discusses factors influencing manufacturing productivity and the properties of cold-bonded aggregate, such as pelletizer disc angle and speed, pelletization duration, water content and the types of raw materials and binders used. The physical properties of cold-bonded aggregates made of different waste materials and binders are presented. The mechanical characteristics, thermal properties and durability of concrete made of cold-bonded aggregates are also reviewed. The literature in the field has established the potential of using cold-bonded aggregates as sustainable materials in the production of normal-weight concrete, as well as structural and nonstructural lightweight aggregate concrete.

Colloidal stability of polymer particles in activator is the pre-condition for the application of polymer dispersion in alkali activated materials (AAM). In this study, investigation of the stability of classical cement-stable polymers (styrene acrylate (SA) and ethylene-vinyl acetate (EVA)) in the presence of sodium silicate with different moduli at varied dosages and storing times was conducted through combined techniques including laser particle analysis and ultraviolet-visible spectrophotometry (UV–Vis). It is found that SA is significantly more stable than EVA dispersions. Dosage of sodium silicate and storing time are the main factors for loss of colloidal stability of the polymer particles. The highest colloidal stability of the latexes was observed with the lowest investigated modulus (M

The present study evaluates the effect of silica modulus on the reaction kinetics, degree of reaction and phase composition of natural pozzolan-based geopolymers. Six natural pozzolan samples have been subjected to geopolymer synthesis in the alkaline medium using sodium hydroxide and sodium silicate solutions at ambient conditions. Reaction kinetics studied by isothermal conduction calorimetry show that the early age dissolution of aluminate and silicate species depends on the SiO2 and Na2O molar content of the alkaline solution. The degree of reaction increases with the reduction of silica modulus. However, the reduction of silica modulus beyond certain limit has a negative influence on the mechanical properties of resultant geopolymers. The optimum silica modulus requirement depends on the mineralogical composition of the raw sample used. The rate of partial dissolution of semi-crystalline and crystalline mineral phases present in natural pozzolan depends on the silica modulus of the alkaline solution used.

Two types of blast furnace slags (HS N and HS V) with different CaO/SiO2 ratios, were activated by potassium silicate solution (Ms = 1). The results showed that most of the alkali silicate activated slag AAS mortars lost their workability within 10 min. Only an AAS mortar made from slag HS V had an outstanding fluidity even after 20 min. The microstructural evolution of the AAS pastes, as well as their selective dissolution residues after 1 h, were analyzed by an ultrasonic method, TGA, FTIR and solid state 29Si/27Al NMR. By employing a model developed for aluminosilicate glasses, Si(Qn(kAl)) species in the slags were calculated and fitted to their 29Si NMR spectra. The results indicate that slag HS V experienced incongruent dissolution during hydration and that its dispersed glass structure in terms of Si(Qn(kAl)) abundance, was significant with respect to its unusual solidification process.

In this study fly ash was milled in three types of mills up to the same median particle size ∼6 µm. The milling was performed in presence of polynaphthalene sulfonate (PNS) superplasticizer and apart of it. It is shown that the introduction of PNS during the milling allows to prevent adverse agglomeration of the particles, while increment of the specific surface area is independent of the presence of PNS. Cement – fly ash pastes prepared with PNS introduced during the fly ash activation exhibit a reduction of the yield stress by 35%, plastic viscosity by 25% and the induction period of hydration by 30% in comparison to the paste prepared with PNS introduced with the mixing water.

In this contribution, the effect of waste magnetite powder (MP), obtained from a rock crushing process, as an additive to cement pastes exposed to elevated temperature and gamma-ray radiation, is evaluated. Cement pastes with different magnetite powder to cement ratios, up to 50% by mass, and exposed to temperatures of 200 °C, 300 °C, 450 °C and 600 °C, were prepared. The thermal conductivity, mass loss, compressive strength and shielding efficiency against gamma-rays (137Cs) of the specimens were determined and the results compared with theoretical values obtained according to the WinXCom program, at different energy levels. The results demonstrate that the addition of MP significantly increases paste density, thermal conductivity, as well as the specific heat of cement stone. Moreover, the inclusion of MP contributes to strength improvements in both heated and unheated states. Likewise, the presence of MP leads to a decrease in mass loss and surface cracking on exposure to high temperature. In conclusion, it is argued that the incorporation of MP results in a significant improvement in gamma-ray shielding properties, as compared to plain cement pastes.

In this study, core-shell structured lightweight aggregates (CSA) were produced through the cold bonding method, by encapsulating an expanded perlite particle (as a core structure) within a shell matrix composed of cement, fly ash and expanded perlite powder. The effect of different curing regimes on the mechanical and microstructural properties of the CSA were studied. To enhance the characteristics of the aggregates produced, they were surface treated by a mixture of cement and silica fume, using two different treatment methods. Afterwards, the properties of lightweight concrete made of either CSA or expanded clay aggregate (ECA) were compared closely in terms of their potential economic and environmental benefits, in response to the high energy consumption associated with the production of ECA. The results revealed that curing at a relative humidity of 99% is the most appropriate curing method for CSA. In addition, treating the CSA surface contributes significantly to enhancing its bulk crushing strength, by about 14–18%. The findings also demonstrate the feasibility of using CSA to produce lightweight aggregate concrete, with a dry density and compressive strength ranging from 1115 to 1540 kg/m3 and from 17.9 to 25.8 MPa, respectively, with a corresponding thermal conductivity range of 0.3169–0.6660 W/m·K.

In order to determine the potential environmental impact of construction products, it is necessary to evaluate their influence on organisms exposed to them or their eluates under environmental conditions. The behavior of the white worm

Extrusion-based additive manufacturing imposes high requirements on the material stability right after the extrusion. Therefore, a thorough understanding of the chemical reactions that determine the early reduction in processability is necessary. Accelerators are especially considered here, which have a major influence on the early reaction. This study contributes to these issues by analyzing the influence of 0.1 wt% TEA (triethanolamine) and 2.0 wt% Ca(NO3)2 on the hydration of two CEM I 52.5 R. The hydration was analyzed by isothermal heat flow calorimetry and in-situ X-ray diffraction. Vicat needle penetration, a penetrometer of own design, and ultrasonic P-wave velocity development were used to monitor the early change in workability. The obtained results indicate that ettringite formation is the main factor influencing workability during the first 60 min of hydration. Afterwards, the influence of ettringite is exceeded by the formation of C–S–H. Ca(NO3)2 was shown to enhance C–S–H formation and had no significant effect on the workability during the first 60 min of hydration while rapidly decreasing workability during the induction period. TEA was shown to increase brownmillerite dissolution and ettringite formation and, consequently, promote the workability loss during the initial hydration period. The time of initial and final setting determined by the Vicat needle test depended mainly on the formation of C–S–H phases.

This study presents a comparison of the effects of micro-Bi2O3 and nano-Bi2O3 powders on the mechanical, microstructural and gamma / neutron shielding properties of Portland cement pastes. Cement pastes with various ratios of cement (up to 30 wt-%) replaced with Bi2O3 micro and nanoparticles were prepared. Consistency, compressive strength, water accessible porosity and mercury intrusion porosimetry tests were performed, in order to characterize their engineering properties. In addition, experimental and theoretical evaluations of γ-ray and neutron shielding properties were performed. The results showed that the incorporation of Bi2O3 powders gradually leads to a decline in cement pastes’ compressive strength and an increase in their porosity, as the amount of powder is increased. However, the deterioration rate varies depending of type of powder used, in favor of nano-Bi2O3. Gamma attenuation tests results indicate that the addition of Bi2O3 powders enhances the shielding capability of pastes, in the energy range of interest (0.08–2.614 MeV). However, the effects of particle size on γ-ray attenuation are negligible in that energy range. Slow neutron attenuation study showed that the addition of nano-Bi2O3 improved the shielding ability of cement pastes, with enhancements ranging between 15.3% and 25.5% for samples with 5 and 30 wt-% nano-Bi2O3, respectively. In conclusion, this study shows that the addition of nano or micro-Bi2O3 is effective in producing lead-free cementitious composites with improved γ-ray and neutron shielding properties. Unlike gamma shielding, nano-sized Bi2O3 has a better ability to attenuate neutrons, in comparison to their micro-sized counterparts.

Copyright © 2021 The Authors. This study investigates the addition of Poly-vinyl Alcohol (PVA) fibres and attapulgite nanoclay to alkali-activated materials (AAMs) with the aim of enhancing the mechanical performance and optimizing the printability and buildability of AAMs. The fresh properties of six mix formulations, including flowability, slump values, rheology, shape retention, and extrusion window, were evaluated. The best performing mixes, that exhibited optimal fresh properties, were 3D printed, and their mechanical performance, microstructure, and buildability were investigated. The addition of 1 wt.-% attapulgite nanoclay (i.e. A-1) showed the desirable fresh properties required for 3D printing, as well as providing sufficient mechanical reinforcement to the samples. The 3D printed A-1 samples showed an improved flexural and compressive strength by 43% and 20%, respectively, compared to both the casted and printed control mixes. Moreover, microstructure analysis, including SEM, Rapidair measurement, and micro-CT, provided evidence of the compatibility by showing the lowest pores anisotropy and mixture homogeneity, between attapulgite and AAMs. European Union's Horizon 2020 research and innovation program under the Marie Skłodowska-Curie grant agreement no. 841592.

This paper presents the results of an interlaboratory study of the rheological properties of cement paste and ultrasound gel as reference substance. The goal was to quantify the comparability and reproducibility of measurements of the Bingham parameters yield stress and plastic viscosity when measured on one specific paste composition and one particular ultrasound gel in different laboratories using different rheometers and measurement geometries. The procedures for both in preparing the cement paste and carrying out the rheological measurements on cement paste and ultrasound gel were carefully defined for all of the study’s participants. Different conversion schemes for comparing the results obtained with the different measurement setups are presented here and critically discussed. The procedure proposed in this paper ensured a reasonable comparability of the results with a coefficient of variation for the yield stress of 27% and for the plastic viscosity of 24%, despite the individual measurement series’ having been performed in different labs with different rheometers and measurement geometries., Deutsche Forschungsgemeinschaft, Projekt DEAL

There are issues on the microstructure characterization of cement paste obtained from μ -CT due to resolution limits, and evaluation of properties through virtual experiments. A phase separation procedure between the solid and pore phases, which can be used for pure cement paste microstructures, is proposed. The problems of underestimation of microstructural characteristics such as porosity in virtual specimens from μ -CT, as compared to real specimens, are addressed. Reflecting such underestimation, the process of input modeling parameter determination for virtual experiments on mechanical property evaluation using the phase field fracture model is elaborated. Through virtual tests, the effects of domain size and mesh resolution on the evaluated properties are investigated, and the correlation between the microstructural characterization parameters and mechanical properties is reconfirmed. It is shown that the virtual experiment framework proposed in this study can be used as a loading tool to supplement time and effort consuming real experiments for evaluating the mechanical properties of cement paste at the micro-scale.

The performance of vacuum insulation panels (VIPs) is strongly affected by several factors, such as panel thickness, design, quality of vacuum, and material type. In particular, the core materials inside VIPs significantly influence their overall performance. Despite their superior insulation performance, VIPs are limited in their widespread use as structural materials, because of their low material strength and the relatively expensive core materials. As an alternative core material that can compensate these limitations, foamed concrete, a type of lightweight concrete with very low density, can be used. In this study, two different types of foamed concrete were used as VIP core materials, with their effects on the thermal behavior of the VIPs having been evaluated using experimental and numerical methods. To confirm and generate numerical models for VIP analysis, micro-computed tomography (micro-CT) was utilized. The obtained results show that insulation effects increase effectively when panels with lightweight concrete are in a vacuum, and both foamed concrete types can be effectively used as VIP core materials.

This study aims to investigate the effects of carbon nanotubes and carbon nanotube-silica core-shell structures, on the behaviour of cement pastes exposed to high temperature (300, 450 and 600 ° C ). Pristine multi-walled carbon nanotubes (MWCNTs) were coated with a solid nanosilica (NS) shell, to form a core-shell nanostructure (MWCNT/NS). The cement pastes were incorporated with three different nanomaterial contents equal to 0.125, 0.25 and 0.5 wt.-% of cement. The results demonstrate that incorporation of an optimum amount (0.125 wt.-%) of MWCNT/NSs, is much more beneficial than the incorporation of MWCNTs, for improving the properties of unheated and heated cement pastes. Silica shell improves the binding ability between cement matrices and nanotubes, which is reflected in specimens’ compressive strength retention, as well as in decreased micro-cracking. However, exceeding the optimum amount of MWCNTs and MWCNT/NSs can lead to an agglomeration of nanomaterial, thus decreasing the thermal resistance of cement pastes.

Lightweight aggregate concrete is a material which has much lower density than normal concrete and many advantages, including advanced insulation performance due to its highly porous or cellular characteristics. Several types of lightweight aggregates have been used to produce lightweight aggregate concrete, and the characteristics of such lightweight aggregates strongly affect the material properties. In this study, three different expanded materials – expanded glass (Liaver), expanded clay (Liapor) and foam glass (Ecoglas) – were utilised as lightweight aggregates, and their effects on the properties of lightweight concrete were investigated. These expanded lightweight aggregates are light and have lower thermal conductivity as well as water absorption than those of normal aggregates. Microstructural characteristics of the specimens with different types of aggregate were examined using X-ray micro-computed tomography. The thermal (thermal conductivity) and mechanical (compressive strength) properties of the lightweight concrete specimens were evaluated experimentally and numerically. The relationship between the physical properties and characteristics was analysed to demonstrate the effect of each expanded aggregate on lightweight aggregate concrete.

Phosphate geopolymers are part of chemically bonded phosphate cements obtained from an aluminosilicate and phosphate solution. Their structure consisting of phosphate bonds makes them suitable for use as refractory material. This study deals with the influence of phosphoric acid concentration (6, 8 and 10 mol/L) on the stability of volcanic ash-based phosphate geopolymers exposed to 100, 600 and 1000 °C. The results reveal that the onset of crystallization is about 600 °C with the formation of aluminum phosphate (V) and tridymite, then crystallization of iron (III) phosphate (V) and hematite at 1000 °C. The degree of crystallization of these phases increases with phosphoric acid concentration. The geopolymers obtained with 8 mol/L of phosphoric acid showed the best thermal stability at 1000 °C in terms of compressive strength change. The maximum thermal linear shrinkage recorded was 3%. The major phases of all geopolymers remain stable up to 1000 °C, after which the melting of phases happens.

Lightweight concrete is a building material used for better insulation and lower energy consumption. The material properties of lightweight concrete, such as compressive strength and thermal conductivity, are strongly affected by the characteristics of its aggregate, binder, and other concrete additions. This study aims to investigate the effects of different concrete additions on the performance of lightweight concrete. Six different materials were used as concrete additions: limestone powder, expanded clay (Liapor®), fine fly ash, fly ash, and fine and normal sand. For lightweight concrete specimens, expanded glass granulate, i.e., Liaver®, was used as a lightweight aggregate to clarify the effects of concrete addition type, with all specimens designed so as to have a density between 800 and 950 kg/m3. The effects of different concrete additions on the characteristics and properties of lightweight concrete were investigated using several approaches; X-ray micro-computed tomography ( μ -CT) was adopted to examine microstructural characteristics, with both the mechanical and thermal properties of the materials being measured using experimental tools. Numerical analysis was also conducted to validate the performance of the materials. The results show that supplementary materials can improve the performance of lightweight concrete with regard to both compressive strength and thermal conductivity.

Natural pozzolans are tremendous source of reactive silica and alumina required for geopolymer synthesis as an alternative binder for ordinary Portland cement. They are available at a comparatively low cost and generate a low ecological footprint through their simple extraction. Following review paper summarizes the mechanical and durability characteristics as well as the microstructural properties of natural pozzolan based geopolymers and their potential as binding material. The microstructural characteristics are based on the advanced analytical techniques used so far to understand geopolymerization, the phase composition, mechanical and durability properties evolution. From this review is obvious that significant analytical techniques have been successfully carried out on fresh and hardened natural pozzolan based geopolymer obtained in alkaline medium, which helped to understand underlying chemical reaction and external factors affecting final properties. These analyses have shown that natural pozzolan based geopolymer has potential to be used as sustainable building materials. But, for its large scale utilisation there is need to upscale the manufacturing process at a pilot-plant in order to address the macroscopic challenges that may arise at that level.

The density of cold-bonded lightweight aggregates is significantly higher than that of sintered lightweight aggregates. Since the sintering technique consumes an enormous amount of energy and emits a huge amount of pollutants, the implementation of a cold-bonded method, in manufacturing low-density lightweight aggregates, is very important from an economic and environmental perspective. In this study, a cold bonding granulation technique was employed to produce low-density lightweight aggregate by the encapsulation of expanded perlite particles in shell structures. A variety of tests were conducted to evaluate the physical and mechanical properties of the aggregate produced. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were used to study the microstructure and the phase composition of the aggregate. Furthermore, X-ray micro-computed tomography (CT) was performed to investigate the pore system of the aggregate specimens. The obtained results showed that by adopting the angle and speed of pelletizer disc, a core-shell structured lightweight aggregates with particle density of 0.88–1.14 g/cm3 and bulk crushing strength of 2.04–2.66 MPa can be produced.

Herein, a new high speed process for microcapsule generation in the field of medium-to-large-size capsules (0.2–5 mm) is reported which is rendered possible by combining three basic processing techniques in one system, namely the coextrusion technique, the vibrational nozzle technique and UV-curing. The versatility of the process is impressing, when it is combined with suitable materials. This is demonstrated for controlled release systems for concrete additives (superplasticizers) based on core–shell as well as matrix-type morphology that are assembled herein. It is shown that the process is highly flexible with respect to the material that can be encapsulated and, moreover, highly adjustable with respect to release mechanisms as these can be steered via the flexible choice of the shell materials. Eventually, the capsules can be created in a highly robust way and at remarkable throughput speed.

In this study, microstructural characterization of various foamed concrete specimens was conducted using multi scale X ray microcomputed tomography micro CT . Foamed concrete specimens with cement only and fine sand or supplementary cementing materials SCMs , such as fly ash and silica fumes, were prepared, which can improve the mechanical properties of the foamed concrete. Various water binder ratios were also considered for each specimen, and pore and solid structures of the foamed specimens were analyzed. Micro CT images with pixel sizes of 24.97 amp; 956;m upper scale and 0.65 amp; 956;m lower scale were combined to investigate the material characteristics. The effects of SCMs on the material characteristics was examined and correlated with the compressive strength of the specimens. The specimens for the upper scale analysis were used to measure the physical properties of the materials, whereas the detailed microstructural characteristics of the specimens were investigated using a lower scale micro CT with relatively small samples. The results from the micro CT at different scales demonstrated that the solid structures in the foamed concrete significantly affected the material strength based on the SCM type and water binder ratio

C-S-H seeding is a promising approach to accelerate cement hydration in a very effective way. Until now little is known about the way the C-S-H seeds work and how they affect the properties of the hydrated cement paste. To be able to analyse this in detail it is necessary to have a preparation method for the C-S-H seeds, which is reproducible and able to prepare seeds with defined properties. The present work describes two methods for the synthesis of C-S-H seeds, a mechanochemical approach and a sol-gel synthesis. A factorial design of experiments setup was used to find those parameters, which affect the efficiency of the C-S-H seeds to accelerate cement hydration and to adjust these parameters in order to achieve the optimized seeds, which are very effective accelerators. Heat flow calorimetry shows that the dormant period of cement hydration can be eliminated by the use of the optimized C-S-H seeds and compressive strength tests show a multiplication of early compressive strength even at very low concentrations of seeds, indicating that an optimization of the synthesis by factorial design of experiments is a promising way for further studies on the mode of action of C-S-H seeds.

Three vinyl acetate ethylene (VAE) latices and incorporated polyvinyl alcohol (PVOH) were investigated. Two of the VAE latices were stabilized by PVOH, while the third was stabilized with an anionic surfactant. The influence of VAE and PVOH on cement hydration was studied by means of isothermal heat flow calorimetry, ICP-OES and in situ XRD measurement. All of the latices prolonged the induction period with an increase in the polymer/cement ratio, whereas the latex stabilized by PVOH hardly influenced the hydration of the silicate phase. Instead, a strong secondary exothermic peak was observed. Based on the in situ XRD analysis, the peak was attributed to the rapid formation of ettringite. Furthermore, the concentration of SO42− in the pore solution was found to have reduced in the presence of polymers in the first hours of the hydration.

Retarders are widely used in construction materials to control the setting and hardening. The present study focuses on changes in the rheological behavior, the admixture adsorption and the pore solution composition with a controlled addition of sodium gluconate and ethylenediamine tetra(methylene phosphonic acid) (EDTMP) in cement. The adsorption of the sodium gluconate was influenced by time of addition of dosage. Delayed addition induced a depot effect which was reduced by the ongoing hydration whereas the adsorption of EDTMP was not affected by time of dosage. Nearly the complete admixture concentration was directly adsorbed on clinker phases or first hydration products. For sodium gluconate, an interaction with ferrite containing clinker phases and a calcium complexing mechanism were suggested. In contrast, EDTMP seemed to have no significant influence on the calcium concentration. With regard to the sodium concentration a fast adsorption of sodium gluconate was determined. Furthermore, a competitive adsorption between dissolved sulfate and retarder molecules or a complex formation mechanism is supposed.

Alkali silica reaction (ASR) occurred in the alkali activated slag (AAS) concrete was evaluated by a revised mortar prism method. The mortars were made of blast furnace slags activated by alkali silicate solution possessing different modulus (0.5, 0.75, 1 and 2) as well as cations (sodium and potassium) and standard sand with a volume replacement of 25 vol% by borosilicate glass beads. Their changes in length and dynamic elastic modulus were monitored up to 7 months. The results showed that ASR has taken place among some mortars, which were evident under both light microscopy and electron microscopy with EDX analysis. The results also revealed that high alkali content did promote the risk of ASR but the degradation due to ASR was affected in a much more complex way.

The aim of this work was an evaluation of the influence of titanium dioxide on the chemical and physical properties as well as the aging behavior of bitumen. Accordingly, two samples of pav...

The RILEM technical committee TC 247-DTA ‘Durability Testing of Alkali-Activated Materials’ conducted a round robin testing programme to determine the validity of various durability testing methods, originally developed for Portland cement based-concretes, for the assessment of the durability of alkali-activated concretes. The outcomes of the round robin tests evaluating sulfate resistance, alkali-silica reaction (ASR) and freeze–thaw resistance are presented in this contribution. Five different alkali-activated concretes, based on ground granulated blast furnace slag, fly ash, or metakaolin were investigated. The extent of sulfate damage to concretes based on slag or fly ash seems to be limited when exposed to an Na2SO4 solution. The mixture based on metakaolin showed an excessive, very early expansion, followed by a dimensionally stable period, which cannot be explained at present. In the slag-based concretes, MgSO4 caused more expansion and visual damage than Na2SO4; however, the expansion limits defined in the respective standards were not exceeded. Both the ASTM C1293 and RILEM AAR-3.1 test methods for the determination of ASR expansion appear to give essentially reliable identification of expansion caused by highly reactive aggregates. Alkali-activated materials in combination with an unreactive or potentially expansive aggregate were in no case seen to cause larger expansions; only the aggregates of known very high reactivity were seen to be problematic. The results of freeze–thaw testing (with/without deicing salts) of alkali-activated concretes suggest an important influence of the curing conditions and experimental conditions on the test outcomes, which need to be understood before the tests can be reliably applied and interpreted.

In order to gain a deeper understanding of the rheological development of hydrating ordinary Portland cement (OPC) pastes at initial state, and to better understand their underlying processes, quantitative X-ray diffraction (XRD) analysis and rheological measurements were conducted and their results combined. The time-dependent relation between phase development and flow behavior of cement paste was investigated at two different temperatures (20 and 30 °C), over a period of two hours. Regarding the phase development during hydration, ettringite precipitation was identified as the dominant reaction in the first two hours. For both temperatures, the increasing ettringite content turned out to correlate very well with the loss of workability of the reacting cement paste. An exponential relationship between ettringite growth and flow behavior was observed that could be explained by applying the Krieger-Dougherty equation, which describes the influence of solid fraction on the viscosity of a suspension.

Cementitious materials have long been used also in hydrothermal conditions, where hydration is significantly different from ambient temperature conditions. The high temperature accelerates mineral dissolution, especially of supplementary cementitious materials (SCMs). This paper reviews the influence of the foreign ions Al3+, Na+, K+, Mg2+, Fe3+ and SO42- dissolved from SCMs and cement clinkers as well as the Ca/Si ratio on the hydration kinetics, including the formation of amorphous C-S-H and its transformation into crystalline phases, and hydrates characteristics under hydrothermal conditions. When SCMs are present under hydrothermal conditions, in addition to the physical parameters, the chemical and mineralogical compositions of the SCMs considerably influences the types and amounts of hydrates. Therefore, the compositions of mixtures can be optimised in order to control the formation rate and sequence of hydrates and their properties.

Basic oxygen furnace slags (BOFS) are by-products of the steelmaking process. Several researchers have studied the production of Portland cement clinker and metallic iron from BOFS via a reductive treatment. In this study, we applied a carbothermal reduction of BOFS in a technical-scale electric arc furnace and characterised the clinker-like products. Those clinker-like non-metallic products (NMPs) had a chemical and mineralogical composition comparable to clinker for ordinary Portland cement (OPC) and contained large elongated alite crystals as major component. The pure NMPs reacted more slowly and achieved a lower degree of hydration compared with commercial OPC. If the reactivity of the products can be further increased by employing specific adaptations, it can be used as a full clinker substitute for OPC. Nevertheless, it is also an option to use the material without further modifications as a cement component or concrete addition, which contributes to the strength development in both cases.

3D printing technology is becoming increasingly important in the construction sector, leading to changes in material requirements compared to traditional manufacturing methods. To characterize the rheological properties (yield stress, viscosity, and structural build-up) of printable mortars, suitable methods are necessary. However, with a rheometer, this is problematic because a time-resolved determination of the properties is complicated, time-consuming, and the torque limitation is often too low. For this reason, a penetration test, and a formula for calculating the yield stress are introduced. To validate the formula, it is determined that the results are comparable with the calculated yield stress based on a rheological test. Furthermore, it is shown that it is possible to extrapolate the data and to determine structural build-up. This paper is intended to give an up-to-date overview of the penetration method and to illustrate the advantages and possibilities of the method in the field of 3D printing. Moreover, it is discussed in which areas improvement and further investigations are needed.

Hydration of cements containing different sulphate carriers, namely gypsum, hemihydrate and anhydrite was investigated with and without triethanolamine. It is found that the hydration of different cements is similar without triethanolamine, but differs significantly with it, which is related to the dissolution rate of sulphate carriers. The initial dissolution of the aluminates is increased by triethanolamine, and the comparatively slow dissolution of anhydrite cannot provide sufficient sulphate to compensate for this enhanced dissolution. This results in an increase of the aluminium species in solution and substantial retardation of C3S hydration. Hemihydrate can suppress this impact due to its high dissolution rate.

Ground granulated blast-furnace slag (GGBFS) is a latent hydraulic binder, which has also the ability to hydrate autonomously after contact with water. The rate of hydration strongly depends on the composition of the slag and the pH-value of the mixing water or activator. The retarded GGBFS suspension and an alkali activator can be used in a special two-component binder system for variable applications. d -gluconic acid (C 6 H 12 O 7 ) was found to be a suitable retarder for GGBFS, which retarded the hydration at least 28 days. The retarder extends the dormant period of the hydration process and prevents mainly the formation of strength-giving phases. The interaction of GGBFS and retarder was investigated by heat flow calorimetry, measurement of non-purgeable organic carbon (NPOC), inductively coupled plasma optical emission spectrometry (ICP-OES), thermogravimetry (TG) and scanning electron microscopy (SEM). The basis for this study was a constant binder content, various concentrations of the retarder and different durations for the retarding effect. The concentrations were 0.05, 0.25 and 1.00% by weight of the mixing water. The samples were investigated between 0 and 28 days. At the end, one mixture was optimized for a shelf time of at least 28 days without separation.