Portland Cement Binders Research Articles

A unified model for predicting the compressive strength of recycled aggregate concrete containing supplementary cementitious materials

Abstract Raising environmental awareness has triggered extensive searching for methods to mitigate impacts of concrete industry on the environment. Feasible solutions include partially replacing nature aggregates by recycled concrete aggregates (RCAs) in new concrete production, and/or using supplementary cementitious materials (SCMs) to substitute a fraction of ordinary Portland cement (OPC) binder. However, SCMs of a given type generally have a broad chemical composition compared to OPC; the inherent inferior properties of RCAs often reduce the mechanical strength of resulting concrete. These two factors pose great challenges to accurately predict the compressive strength of concrete containing SCMs and RCAs. In this study, a unified model is proposed by considering the reactivity of SCM and the physical characteristics of RCAs in a concrete mix and calibrated based on an extensive experimental database containing 654 individual datasets. The proposed model predicts the compressive strength of recycled aggregate concrete containing SCMs not only with a good accuracy but also with strong chemical and physical senses, hence providing a useful design tool and, ultimately, promoting application of such green concrete products and contributing to experimental friendliness.

The role of the crystallo-chemical factor in the evaluation and improvement of the nanomodification efficiency of mortar and concrete

The article presents a new approach to the control of the processes of structure formation of binder systems, taking into account the achievements of nanotechnologies. The possibilities of managing the structure of the material at the nanoscale and the micro-level by introducing primary nanoscale additives or forming nanoscale objects in the bulk of the material are considered. The peculiarities of contact zone formation and microstructure of artificial stone based on nanomodified Portland cement and alkaline binder systems are investigated. The role of the crystallo-chemical factor and its influence on the strength formation of all levels of concrete structure are shown. It is proved that when using micro silica modifying additives, their efficiency at the micro level is higher than at the meso- and macro-levels. At the same time, the modification of the binding systems by artificial zeolites provides a more pronounced effect in concrete at the macro-level – due to the crystallo-chemical similarity of additives, products of hydration and minerals of the aggregate. Taking into account the crystal-chemical similarity of the new formation opens new possibilities for the choice of nano additives, considering not only the principle and nature of their action at the level of nanoscale and microstructure, but also the influence on the peculiarities of the formation of the contact zone at the meso- and macro-levels, which will have a decisive influence not only on the strength, but also on the special properties of concrete.

Recycled geopolymer aggregates as coarse aggregates for Portland cement concrete and geopolymer concrete: Effects on mechanical properties

The available literature on recycling of geopolymer concrete is currently limited to application of recycled geopolymer aggregates as coarse aggregates for new geopolymer concrete. This paper highlights an alternative waste management strategy for geopolymer concrete construction and demolition waste by illustrating the suitability of recycled geopolymer aggregates for full or partial replacement of coarse natural aggregates in the widely used Portland cement concrete. The properties of Portland cement concrete and geopolymer concrete made with varying contents of coarse geopolymer recycled aggregates (0%, 20%, 50% and 100% coarse natural aggregates replacement) are investigated and compared with those of Portland cement concrete containing recycled Portland cement concrete aggregates. The results indicate that up to 20% replacement of coarse natural aggregates with recycled geopolymer concrete aggregates results in only insignificant reductions in the modulus of elasticity, flexural strength and volume of permeable voids as well as a moderate reduction in compressive strength of Portland cement concrete. The negative effects of varying amounts of recycled geopolymer concrete aggregates on the properties of Portland cement concrete is however found to be slightly more significant than those caused by same proportions of recycled aggregates produced from Portland cement concrete waste. Furthermore, incorporation of coarse recycled geopolymer concrete aggregates is found to lead to more significant negative effects on properties of Portland cement concrete than geopolymer concrete. These include respectively 21%, 8.3% and 3.4% further reductions in compressive strength, modulus of elasticity and flexural strength of RAGC compared to RAG at 100% coarse aggregate replacement ratio, highlighting a higher compatibility between geopolymer recycled aggregates and geopolymer binder than Portland cement binder.

Lightweight concrete with expanded aggregate from siliceous rocks

The purpose of this study is to develop technology for the production of a new building composite made of silicon-containing rocks. An aggregate is foamed granules obtained on the basis of diatomite with the addition of caustic soda, dolomite, water and liquid glass. The material composition, materials processing, physical and mechanical properties have been observed. The problem of alkali-silicate interaction typical for traditional Portland cement and glass phase is solved through the use of magnesia binder. Samples on Portland cement and magnesia binder were obtained, the aggregate content was varied. Some aggregate fractions were used to obtain high packing density in the composite. Concrete was estimated according to density, compressive strength and tensile strength, water absorption and thermal conductivity. Analysis of the material structure was made. The results of the study of the microstructure of synthesized concrete indicate the presence of a cement matrix in which granules of various sizes are tightly packed. The results of X-ray phase analysis of synthesized concrete indicates that the cement matrix consists of forsterite crystals. Approximate savings in the use of concrete with the developed aggregate is about 10-20%. Such savings are possible due to the fact the surface occurrence of siliceous rocks allows them to be mined in an open way with minimal costs compared to other rocks, with a lower calcination temperature during material creation.

Characteristics of geopolymer hybrid concrete in peat water

Geopolymer hybrid is a combination of geopolymer and Ordinary Portland Cement (OPC) or other binders to produce an alternative binder. This type of binder could be used to transform low-quality fly ash into multi-purpose concrete. Ordinary Portland Cement (OPC) concrete subjected to an acidic organic environment such as peatland, is more prone to deterioration in long-term than concrete using the supplementary cementitious material. In this research, the geopolymer was made by activating low-quality fly ash (contains more than 5% carbon) with the alkaline activator. The inclusion of OPC and Portland Cement Composite (PCC) as a fly ash replacement material is intended to promote curing at ambient temperature and immobilization of heavy metals in fly ash. The specimens were cast and cured at ambient temperature up to 28 days. OPC was used as a control mix. Subsequently, the concrete was immersed in fresh peat water in the laboratory up to 28 days. Characteristics of the geopolymer hybrid such as compressive strength, porosity, and leaching were determined. Microstructure analysis, such as SEM-EDX and FTIR, were conducted. Results show that the geopolymer hybrid has a good strength development at early days. At 28 days, there was a reduction of strength and increase of porosity, probably due to the attack of calcium from the OPC concrete. There was a transformation of aluminosilicate gel into C/N-A-S-H that is advantageous for the strength development at the early days. However, a weaker material has formed in the long term that cannot resist further acid attack. It can be concluded that the geopolymer hybrid is a promising binder, but it is essential to design the material appropriately to have better strength, durability and environmental properties in the long term.

Machine learning can predict setting behavior and strength evolution of hydrating cement systems

AbstractSetting and strength development of ordinary Portland cement (OPC) binders involves multiple interacting chemical reactions, resulting in the formation of a solid microstructure. A long‐standing yet elusive goal has been to establish a basis for the prediction of the properties and performance of concrete using knowledge of the chemical and physical attributes of its components—PC, sand, stone, water, and chemical admixtures—together with the environmental conditions under which they react. Machine learning (ML) provides a data‐driven basis for the estimation of properties, and has recently been applied to estimate the 28 days (compressive) strength of concrete from knowledge of its mixture proportions (Young et al, Cem Concr Res, 2019, 115:379). Building on this success, the current work uses a diverse dataset of ASTM C150 cements, the chemical composition and other attributes of which have been measured. ML estimators were trained with this dataset to estimate both paste setting time and mortar strength development. The ML estimation errors are typically similar to the measurement repeatability of the relevant ASTM test methods, and are thus able to account for the influence of binder composition and fineness. This creates new opportunities to apply data intensive methods to optimize concrete formulations under multiple constraints of cost, CO2 impact, and performance attributes.

Bioactive Additives for Self-Healing of Concretete Microstructure

As a result of the influence of the corrosive environment, the construction materials have a decrease in performance. To increase the service life of the structures, continuous monitoring and, if necessary, restorative repairs are carried out. One of the ways to maintain the initial properties for materials is to give them a self-healing effect by introducing a specially developed additive containing a bioactive component in the manufacturing process. The article presents the results of research on the ability of building materials based on mineral binders to self-repair. Mixtures containing nutrient medium for the biomass of aerobic bacteria were used as bioadditives. Portland cement and gypsum binder were used as mineral binders. The obtained results allow to make a conclusion about a significant change in the rheological properties of cement-sand mortars due to the presence of biological surface-active substances that are part of the cells of microorganisms. The effect of changing the concentration of cells on the setting time and on the strength characteristics of cement-sand mortars was established.

Behaviour of environment friendly green concrete beams using fly ash and furnace slag under cyclic loading

This paper investigates an alternative binder to Portland cement binder which is very friendly to environment as Portland cement emits 0.8 ton to 1.0 ton of greenhouse gas (CO2) during the production of 1.0 ton of cement. To test the suitability of GPC against RCC for structural applications, four beams of size 125 mm × 250 mm × 3,200 mm were cast. Two for reinforced cement concrete (RCC) which act as control beams (CB) and two for GPC. The beams were tested up to failure under monotonic as well as cyclic loading in a reaction frame under displacement control to study the flexural cyclic behaviour.

Monitoring the Carbonation-Induced Microcracking in Alkali-Activated Slag (AAS) by Nonlinear Resonant Acoustic Spectroscopy (NRAS)

Abstract This article presents the potential of nonlinear resonant acoustic spectroscopy (NRAS) for noninvasive monitoring of the carbonation progress in alkali-activated slag (AAS) mortars. In the search for sustainable concrete, AAS has emerged as a potential substitute for ordinary portland cement binder. However, carbonation is reported to be an important durability concern for AAS due to the absence of portlandite. In this study, the correspondence between the physical properties and microstructural evolution of sodium silicate-activated slag (SS-AS) and sodium hydroxide-activated slag (SH-AS) mortars were studied over the full course of accelerated carbonation. The measured properties include the following: compressive strength, carbonation depth, porosity, pore size distribution, and phase assemblage. In addition, NRAS was used to track the changes in materials stiffness (linear resonance frequency) and hysteretic nonlinearity (amplitude dependency of resonance frequency). Scanning electron microscopy (SEM) images and porosimetry results showed the formation of microcracks and increased micrometer porosity in a carbonated AAS binder caused by calcium aluminum silicate hydrate decalcification; the cracking was more severe in the SS-AS than in the SH-AS. The NRAS results revealed a close correspondence between the observed microscopic changes in the samples and measured macroscopic test parameters, indicating the potential of acoustic techniques for monitoring the advancement of carbonation fronts in AAS mortars.

Unsaturated behaviour of a stabilized marine sediment: A comparison of cement and GGBS binders

In order to ascertain the contaminant-encapsulation potential of stabilized soil, an understanding of its unsaturated hydraulic behaviour, specifically the Soil Water Retention Curve (SWRC), is paramount. In this paper, centrifuge testing was used to obtain SWRCs for sediment dredged from an Irish harbour, stabilized with Ordinary Portland cement (OPC) and Ground Granulated Blast Furnace Slag (GGBS) binders. The effects of the different binder proportions and different curing times on both the Unconfined Compressive Strength (UCS) and SWRC were investigated, with the support of Scanning Electron Microscope (SEM) data. The Fredlund and Xing (1994) empirical model was found to provide the best fit to the stabilized sediment SWRCs. The water holding capacity was found to increase with increased binder content, increased GGBS proportion in the binder and increased curing time, suggesting that high-GGBS binders are most suitable for locking in contaminants. An examination of relationships between one of the model parameters (Air Entry Value, AEV) and UCS further highlights differences in strength and water retention mechanisms between the two binder combinations. In addition to its well-known environmental credentials, this research highlights the technical merits in using GGBS in contaminated sediment reuse projects.

Evaluation of Marshall Stability Design Principles: Applied to Cold In-Place Recycling

The objective of this paper is to document limitations and robustness issues with Marshall stability (MS) testing for cold in-place recycling (CIR) mix designs. This paper focuses efforts on MS because many departments of transportation are using this test for CIR design, and the data presented in this paper supports abandonment for any type of CIR mix design. Unconfined compressive strength (UCS) and indirect tensile strength data is used throughout the paper for benchmarking, as both tests are used in various capacities for in-place recycling designs. Portland cement and asphalt emulsion binders were assessed in this paper. In comparison with UCS design curves with cement, MS results for emulsion were not as rational and often did not respond to emulsion content changes in a logical manner. MS repeatability was poor for the materials evaluated in this paper. Replicate design curves ranged from all points below a design threshold (i.e., all emulsion dosage levels failed to meet the design criteria) to all points above a design threshold (i.e., all emulsion dosage levels successfully met the design criteria). The typical minimum MS criteria (5.56 kN) was exceeded without any emulsion for specimens oven conditioned for 2 h at 40°C. A notable limitation of the data presented in this paper was that retained MS (i.e., assessment of moisture conditioning effects) was not performed comprehensively throughout the work.

Effect of slag content and activator dosage on the resistance of fly ash geopolymer binders to sulfuric acid attack

Geopolymer (GP) binders are an appealing alternative to Portland cement (PC) binders as they have the potential to reduce the CO2 emissions associated with the cement and concrete industry. However, their durability in aggressive environments needs thorough examination if they are to become a viable alternative to traditional PC materials. This study investigated the effect of increasing slag content and activator dosage on the sulfuric acid resistance of fly ash GP binders. Their performance was also compared with that of neat PC mixes using various physical and microstructural techniques. The results show that increasing the slag content of fly ash GPs decreases porosity, but makes the reaction products more susceptible to sulfuric acid attack. It was also found that increasing the alkaline activator dosage of fly ash GPs has little impact on sulfuric acid resistance. Finally, GP binders displayed superior sulfuric acid resistance than their PC counterparts.

A model investigation of the mechanisms of external sulfate attack on portland cement binders

A recent microstructural model for simulating external sulfate attack on cement paste is used to calculate the driving force for local expansive growth of AFt phase in terms of crystallization pressure, and the strain and stress fields are tracked within the microstructure with micrometer-scale resolution using a linear elastic finite element model. Damage induced by expansion modifies both the local effective transport properties and linear elastic properties of each microstructure at different depths, and thereby potentially alters the rates of sulfate ingress and expansion. Simulations give insight about sulfate attack mechanisms, which are investigated in more detail by separating the individual influences of sulfate concentration and pH of the pore solution. Especially when soluble carbonates are present, reductions in the pore solution pH, which often accompany ingress of sulfates, significantly destabilizes calcium monosulfoaluminate and accelerates AFt growth. In fact, within a narrow pH range some calcium monosulfoaluminate can spontaneously transform to AFt without any additional sulfate addition. Therefore, the progress of phase transformations and expansion from the surface to the interior of the porous material is dictated by the rate of ingress of concentration fronts of both sulfate ions and pH, which do not necessarily coincide.

Comparison of chloride permeability methods for Alkali-Activated concrete

This paper presents the results of an experimental study of chloride permeability in alkali-activated fly ash, alkali-activated slag, and Portland cement concrete. Test methods include the rapid chloride permeability test (RCPT), AC and DC electrical resistivity, and the 90-day salt ponding test. We hypothesize that differences in pore solution chemistry between alkali-activated and Portland cement binders render electrical methods unable to accurately estimate chloride permeability in alkali-activated concrete. The present study seeks to evaluate this hypothesis by comparing results from electrical tests with diffusion coefficients from salt ponding tests. Contrary to previous claims, the RCPT provided a good estimate of chloride permeability in both alkali-activated slag and alkali-activated fly ash concrete. RCPT results showed excellent correlation with diffusion coefficients determined from salt ponding tests. Resistivity-measurements exhibited poor correlation to diffusion coefficients and overestimated the resistance to chloride ion penetration. Furthermore, AC and DC resistivity measurements showed significant disagreement for alkali-activated concrete. Finally, evidence form salt ponding tests suggests differences in chloride binding potential between alkali-activated and Portland cement concretes.

Полистиролбетон на портландцементном вяжущем с добавлением жидкого стекла и шамота

Полистиролбетон на портландцементном вяжущем с добавлением жидкого стекла и шамота

Influence of alkali solutions on properties of pond fly ash-based geopolymer mortar cured under different conditions

Waste management of pond fly ash containing heavy metals beyond optimum limit is essential, otherwise leaching in the soil, water and air will create many hazardous problems. The best way to utilise pond fly ash is to convert it into geopolymer cement. Geopolymers form a class of binders manufactured by activation of solid aluminosilicate source material with a highly alkaline activating solution and aided by thermal curing. In the past few decades, geopolymer binders have emerged as one of the possible alternatives to ordinary Portland cement binders due to their reported high early strength and resistance against acid and sulfate attack apart, from their environmental friendliness. An experimental study was conducted to assess the activating influences of the combination of different alkali hydroxides and silicates (NaOH/Na2SiO3, NaOH/Li2SiO3, KOH/Na2SiO3 and KOH/Li2SiO3) on the mechanical properties of mortars. Geopolymer mortars using sand were cured at 80°C for 4, 8 and 12 h and compressive strengths were determined. Curing was also done by heating in a microwave oven for 10, 20, 30, 40, 50 and 60 min and compressive strengths were determined. Results for compressive strengths in the presence of different combinations of alkalis were compared.

Compressive strength and microstructure of alkali-activated fly ash/slag binders at high temperature

This paper reports the results of the compressive strength and microstructure of various alkali-activated binders at elevated temperatures of 300 and 600 °C. The binders were prepared by alkali-activated low calcium fly ash/ground granulated blast-furnace slag at ratios of 100/0, 50/50, 10/90 and 0/100 wt.%. Specimens free of loading were heated to a pre-fixed temperature by keeping the furnace temperature constant until the specimens reached a steady state. Then the specimen was loaded to failure while hot. XRD, SEM and FTIR techniques were used to investigate the microstructural changes after the thermal exposure. The fly ash-based specimen shows an increase in strength at 600 °C. On the other hand, the slag-based specimen gives the worst high-temperature performance particularly at a temperature of 300 °C as compared to ordinary Portland cement binder. This contrasting behaviour of binders is due to their different binder formulation which gives rise to various phase transformations at elevated temperatures. The effects of these transformations on the compressive strength are discussed on the basis of experimental results.

Thermal performance of calcium-rich alkali-activated materials: A microstructural and mechanical study

The effects of Si/Al, Na/Al and water/solids ratios on thermal performance of alkali-activated materials (AAM) based on fly ash-slag blends are investigated. Higher Na/Al decreased compressive strength but increased post-heated strength retention and mass loss while reducing cracking at 1000°C. Lower Si/Al resulted in lowest initial strength but highest thermal stability, with an increase in strength after exposure to 1000°C, while a high degree of cracking was observed at higher Si/Al ratio. The effect of w/s on thermal performance was subtle. Computed tomography analysis showed for the first time thermally induced expansion of pores which reduced surface cracking via water vapour pressure release. Thermal performance of alkali-activated materials (AAM) is significantly better than Portland cement (PC) of the same compressive strength because of the very low bound water content. The porosity, pore connectivity and number of pores of the AAM were considerably higher than those in the PC binder.

CHANGES OF CONSTRUCTION MATERIAL PROPERTIES WITH ADDITION OF BACTERIAL CELL BIOMASS POSSESSING UREASE ACTIVITY INTO THE MATERIALS

Results of research that aimed on appearance of self-healing ability between characteristics of construction materials and products, based on mineral binding substances, via bioprocesses of selective action, resulting from the introduction of bacterial biomass into the composition of mortar and consruction cement mixes were shown in the article. The article contains the results of revealing the most active forms of biological material adapted to the conditions of formation of building products based on mineral binders and results of investigating their effect on the rheological, technological and operational properties of mortars that are modified. Portland cement and gypsum binder were used as mineral binders to produce solution mixtures with different pH values. Efficiency of bacterial cell action was determined via estimation of cell urease activity. The variations of values of water-cement ratio appeared to be pronounced in dependence on: concentrations of introduced cell biomass content; changes in the urease activity of the bacterial cells, varied with the values of pH of used medium; the use of both highly porous natural and artificial materials as microcontainer carriers. The obtained results make it possible to conclude about significant change in the rheological properties of cement-sand mortars owing to the presence of biological surfactants entering into a content of bacterial cells. The influence of cells concentration on a setting time and strength characteristics of cement-sand mortars was determined.

Interactions of Various types between Rock and Alkali-Activated Blast Furnace Slag

Abstract Alkali-activated binders (AAB) are very intensively studied materials nowadays. Because of possible usage as secondary raw materials, they can be environmentally efficient. Intensive research is focused especially on binder matrix, composition and its structure. For industrial usage, it is necessary to work with some aggregate for the preparation of mortars and concretes. Due to different structures of alkali-activated binders, the interaction with the aggregate will be different in comparison to an ordinary Portland cement binder. This paper deals with the study of interactions between several types of rocks used as aggregate and alkali-activated blast furnace slag. The research was focused especially on mechanical properties of prepared mortars.