Ordinary Portland Cement Systems Research Articles

Impact of exposure conditions on alkali-silica reaction in alkali-activated material systems

The influence of different testing methods on alkali-silica reaction (ASR) behavior is a result of the difference in the effect of exposure conditions on it. This study investigated the impact of temperature and the addition of alkali on ASR behavior in an alkali-activated material (AAM) system and compared it with an ordinary Portland cement (OPC) system. The results showed that the ASR in the AAM system was more independent of the exposure conditions than that in the OPC system because of its inherently high alkalinity and dense microstructure. More ASR products with higher Na:Si ratios were evident in the alkali-activated slag (AAS) mortars than in the OPC mortars. The accelerated test conditions developed for OPC systems could be applied to AAM systems. However, owing to the difference in the acceleration effect, comparing the ASR-induced expansion in OPC and AAM systems using the accelerated test method was misleading to some extent. This study contributes to the understanding of the ASR in AAM systems and is of considerable importance for the industrial application of AAMs.

Feasibility of adding calcium hydroxide to FETNS–OPC: working performance, mechanical properties and reaction mechanism

To solve the problem of low early-phase reactivity of ferrous extraction tailings of nickel slag (FETNS), the effects of calcium hydroxide (Ca(OH)2) as an alkali activator on the working performance, mechanical properties and hydration products of FETNS–ordinary Portland cement (OPC) composite cementitious systems were studied. The addition of calcium hydroxide was found to shorten the initial setting time by about 40% and the final setting time by about 20%. The compressive strength at 3, 7, 28 and 60 days was increased by 51.95%, 45.27%, 8.53% and 8.9%, respectively, with the addition of calcium hydroxide. Microstructural assessment (by scanning electron microscopy, X-ray diffraction, simultaneous thermal analysis, nitrogen adsorption test and low-field nuclear magnetic resonance analysis) showed that the incorporation of calcium hydroxide increased the reaction degree of the FETNS–OPC system, and more calcium silicate hydrate gel and ettringite were generated to fill internal pores, thus improving the compactness of the matrix. In summary, the incorporation of calcium hydroxide stimulated the early-phase reactivity of the composite system, promoted the formation of reaction products and optimised the internal pore structure.

Natural carbonation of portland cement with synthetic zeolite Y as a supplementary cementitious material

Risks associated with carbonation are a key limitation to greater replacement levels of ordinary portland cement (OPC) by supplementary cementitious materials (SCMs). The addition of pozzolanic SCMs in OPC alters the hydrate assemblage by forming phases like calcium-(alumina)-silicate-hydrate (C-(A)-S-H). The objective of the present study was to elucidate how such changes in hydrate assemblage influence the chemical mechanisms of carbonation in a realistic OPC system. Here, we show that synthetic zeolite Y (faujasite) is a highly reactive pozzolan in OPC that reduces the calcium content of hydration products via prompt consumption of calcium hydroxide from the evolving phase assemblage prior to CO2 exposure. Suppression of portlandite at moderate to high zeolite Y content led to a more damaging mechanism of carbonation by disrupting the formation of a passivating carbonate layer. Without this layer, carbonation depth and CO2 uptake are increased. Binders containing 12–18% zeolite Y by volume consumed all the calcium hydroxide from OPC during hydration and reduced the Ca/(Si+Al) ratio of the amorphous products to near 0.67. In these cases, higher carbonation depths were observed after exposure to ambient air with decalcification of C-(A)-S-H as the main source of CO2 buffering. Binders with either 0% or 4% zeolite Y contained calcium hydroxide in the hydrated microstructure, had higher Ca/(Si+Al) ratios, and formed a calcite-rich passivation layer that halted deep carbonation. Although the carbonated layer in the samples with 12% and 18% zeolite Y contained 70% and 76% less calcite than the OPC respectively, their higher carbonation depths resulted in total CO2 uptakes that were 12x greater than the OPC sample. Passivation layer formation in samples with calcium hydroxide explains this finding and was further supported by thermodynamic modeling. High Si/Al zeolite additives to OPC should be balanced with the calcium content for optimal carbonation resistance.

Experimental and theoretical studies on the hydration of ordinary portland cement/calcium sulfoaluminate cement blends containing biological admixtures

The present study investigated the hydration properties of ordinary portland cement (OPC) and calcium sulfoaluminate (CSA) cement blends with the biological admixtures to examine the feasibility of the blends as a carrier for microbes, Sporosarcina pasteurii. The hydration kinetics of the blends were explored by X-ray powder diffractometry, thermogravimetry, and 27Al nuclear magnetic resonance analysis. The test outcomes revealed that the blended CSA cement expedited the early hydration of OPC clinker, which was delayed by the biological admixtures in the sole OPC system. In particular, blending with the CSA cement improved rapid strength development, lowered pH, and increased the crack healing capacity. Furthermore, the hydration of the systems was thermodynamically modeled to provide the fundamental idea of the systems and to compare with experimental phase assemblages. The hydration kinetics and development of physical and chemical properties of the blends were simulated and discussed along with the experimental data.

Investigation on foam stability of multi-component composite foaming agent

The multi-component composite foaming agent (CFA) with excellent properties was prepared by sodium α-alkenyl sulfonate (AOS), sodium dodecyl sulfate (K12), coconut oil (CO), and rosin liquid (RL), and three foam stabilizers, namely hydroxypropyl methylcellulose ether (HPMC), xanthan gum and sucrose. The foam stability and the foam stability in an alkaline environment and slurry were studied. The results show that the optimal composition of the multi-component CFA is 0.4% AOS, 0.1 % K12, 0.2% RL, 0.3% CO, 0.08% HPMC, 0.6% xanthan gum and 0.6% sucrose. When the CFA is used to prepare foam, the foaming multiple (FM) is 41, and the 1-hour settlement distance (SD) and the 1-hour bleeding ratio (BR) are zero. Moreover, the foam can maintain excellent stability within 2 h. Under an alkaline environment, when the pH is higher than 12.4, the foam stability will be adversely affected. The effective foam ratio (EFR) of foamed concrete increases first and then decreases with the increase of foam content. When foam content is less than 2.8 L/kg, the foam stability in ordinary Portland cement (OPC) paste is better than that of alkali-activated slag (AAS) paste. When the foam content is higher than 2.8 L/kg, the foam stability of the latter is better than the former. When foam content is 2.8 L/kg, the apparent density OPC and AAS system is 698 kg/m3 and 623 kg/m3, respectively. Compared with OPC foamed concrete, AAS foamed concrete presents more small pores, smaller average pore size and better roundness.

3D printing of limestone-calcined clay cement: A review of its potential implementation in the construction industry

The rapid development in 3D printing applications requires exploring a sustainable printable mixture to decrease the environmental impact induced by the existing Ordinary Portland Cement (OPC) mixtures and enable 3D printing technology to reach its peak efficiency. The high-volume substitution of OPC with supplementary cementitious materials (SCMs) is of significant interest as a promising solution for developing low-carbon feedstock for 3D printing. Yet, those materials share the problem of limited availability. The combination of limestone and calcined clay could be a promising alternative, offering various benefits, including replacing OPC in high ratios. This paper reviews 3D printable limestone calcined clay cement (LC3) mixtures, compositions, and chemical behaviour. The effect of different sand-to-binder ratios, additives content, OPC replacement levels, clay grade and calcination, and admixtures on the fresh, hardened and printing properties of the 3D printed mixtures are critically discussed. The environmental impact and production cost of the LC3 system compared to OPC and other systems are also critically evaluated along with the applications, future directions and research gaps in this field. The findings of this review show that 3D printed LC3 has a similar hardened performance and better microstructure than OPC system. Moreover, cast LC3 system has 30–50% lower environmental impacts depending on the replacement level and better economic feasibility than OPC. Therefore, making it a suitable feedstock for the innovative manufacturing technology of 3D printing.

Alkali-silica reactivity of lightweight aggregates in alkali-activated slag cement and ordinary Portland cement systems

For alkali-activated slag cement (AAC), an environmentally-friendly material, high-alkalinity activators are normally utilized for activation, which can lead to possible concrete degradation owing to alkali-silica reaction (ASR) when alkali-active aggregates were used. This study explored the effectiveness of lightweight aggregates in mitigating ASR behaviors of the AAC system. Alkali-reactive expanded perlite and non-alkali-reactive expanded shale were used as lightweight aggregates to compare ASR behaviors in ordinary Portland cement (OPC) and AAC systems. The formation of ASR gel in the expanded perlite was expansive, whereas the higher Ca/Si ratio calcium-aluminate-silicate-hydrate (C-A-S-H) in the non-alkali-reactive expanded shale did not cause expansion. In contrast with the OPC system, the larger amount of lower Ca/Si ratio ASR gel caused more deleterious ASR expansion and cracks in the AAC system. Furthermore, replacing expanded perlite with expanded shale effectively mitigated the ASR expansion. Discussion on the ASR mitigation mechanism of lightweight aggregates was provided for predicting the influence on the concrete.

Effect of hydration assemblage on the autogenous shrinkage of alkali-activated slag mortars

The purpose of this work is to characterise the autogenous shrinkage performance of alkali-activated slag (AAS) mortars prepared with four activator types (i.e. sodium hydroxide, waterglass, calcium hydroxide/sodium carbonate and calcium oxide/sodium carbonate), with ordinary Portland cement (OPC) mortar as the reference sample. The hydration assemblage and nanostructure of calcium aluminosilicate hydrate (C-A-S-H) were investigated using a series of microscopic characterisations, including X-ray diffraction (XRD), thermogravimetric analysis (TGA) and silicon-29/aluminium-27 nuclear magnetic resonance (29Si/27Al MAS NMR) analysis combined with thermodynamic modelling. The results show that the autogenous shrinkage of mortar samples is highly associated with C-A-S-H type and mass content in the cementitious systems. Compared with the OPC system, the larger C-A-S-H mass fractions in AAS systems affect the microstructure rearrangement, contributing to higher autogenous shrinkage. Furthermore, the autogenous shrinkage in AAS systems is negatively correlated with the medium chain length and aluminium (Al) incorporation degree of C-A-S-H.

Assessing the critical chloride threshold of conventional reinforcement embedded in alternate cementitious systems

Alternate cementitious materials (ACMs), such as calcium aluminate cements (CAC) and calcium sulfoaluminate cements (CSA), contain lower embodied energy and carbon footprints when compared to traditional ordinary portland cement (OPC) systems. However, the sustainability of these ACM systems can be nullified by a lack of durability and/or resiliency. To develop an understanding of the durability and long-term performance of the ACMs, standardized test methods are required to assess their corrosion resistance. OCcrit, a new test method that was developed at Oregon State University, is a fast and reliable method to study the corrosion performance of cementitious systems. This method, however, has only been evaluated using OPC systems. In the first part of this study, testing was performed to potentially extend the applicability of this new test method to CAC and CSA systems, thereby increasing its robustness and value. In the second part of the study, the updated OCcrit method was used to assess the critical chloride threshold of steel reinforcement embedded in CAC and CSA systems. Results indicate that CSA specimens exhibit lower critical chloride threshold values than OPC and CAC specimens and the critical chloride threshold of the CAC seems to be dependent on the water-cementitious materials ratio.

Mechanism understanding of alkali-silica reaction in alkali-activated materials system

To provide a better understanding of the mechanism of alkali-silica reaction (ASR) in alkali-activated materials (AAMs) system, in this work, the ASR behavior of alkali-activated slag (AAS)/fly ash (AAFA) mortars were investigated, and compared with ordinary Portland cement (OPC) mortars. It is found that although the AAS mortar bars experience the shrinkage first, the onset of ASR-induced expansion of AAS mortar bars is earlier than OPC mortar bars. In AAMs system, the reactive silica from aggregates is evidently dissolved and participated in the early-age alkali-activation, and thereby leads to the reduction of reactive silica for ASR. The Ca/Si ratio of amorphous ASR products in AAS mortars was lower, while Al/Si and Na/K ratios were higher than that of OPC mortars. Based on the obtained experimental evidences, a conceptual model was proposed to interpret and compare the ASR behavior in OPC, AAS and AAFA systems.

Geopolymer as the future oil-well cement: A review

The petroleum and cement manufacturing industries have been accused of contributing substantial quantities of carbon dioxide (CO 2 ) into the atmosphere. Additionally, Portland cement systems suffer carbonation and degradation in high saline and acidic environments. Geopolymer, a much cleaner cementitious binder, synthesized through the reaction of aluminosilicate materials and alkaline solution has been a leading alternative to ordinary Portland cement (OPC). The feasibility of using geopolymer in oil-well cementing is still being explored. The objective of this review study is to provide a single document that summarizes the findings from these studies. In general, researchers have explored geopolymer application in aggressive environments and well plug and abandonment operations, the effect of temperature, and its compatibility with drilling fluid. Compared to OPC systems, geopolymer is more resistant to acidic environments, performs better in high saline conditions, and is highly compatible with drilling mud. The geopolymer being a green technology coupled with its optimized properties implies that it is the future of oil-well cement. For further studies, we suggest in-depth characterization of lightweight geopolymers. • The state of research on the application of geopolymer for oil well cementing has been explored. • Geopolymer overcomes many of the issues faced with ordinary Portland cement (OPC). • Geopolymer would be an excellent alternative to OPC-based systems.

Retention of strontium in high- & low-pH cementitious matrices – OPC vs. model systems

Strontium can be found in low/intermediate level radioactive waste streams, often solidified by Ordinary Portland Cement (OPC) matrices. Amorphous silica is added to improve wasteform performance, leading to low-pH systems. Our aim is to identify the phases controlling strontium immobilization in OPC matrices. The novelty of this work resides in combination between two approaches: 1) Comparing OPC systems to model systems based on alite, yielding matrices containing only major phases, emphasizing the relative role of minor phases; 2) Comparing high- & low-pH pastes. Pastes were characterized using calorimetry, XRD, DTG, SEM/EDS and porosimetry. Leaching experiments were conducted to study Sr retention and diffusivity. Strontium diffusivities in low-pH pastes are lower with respect to high-pH equivalents, despite their higher porosities, due to preferred Sr sorption to low Ca/Si C-S-H. OPC pastes show better Sr retention relative to model systems, suggesting that minor phases (like ettringite and AFm) improve Sr retention.

Alkali-activated concrete mixes with ground granulated blast furnace slag and paper sludge ash in seawater environments

Predicted sea level rise due to global warming will necessitate the construction of coastal defenses to protect the populations in the vicinity of the coasts. Large quantities of concrete will be required with consecutive increases in greenhouse emissions, hence an increasing need for alternative to Ordinary Portland Cement (OPC) cements. Feasible potential alternatives could be found in alkali-activated cements, which also include industrial by-products or waste materials. This paper presents a laboratory study of concrete mixes based on the alkali-activation of an industrial by-product, ground granulated blast furnace slag (GGBFS) and includes an industrial waste, paper slugde ash (PSA) in the alkali-activator mixes. The use of seawater as mixing and curing water was also examined. The compressive strength and a number of durability-related properties of alkali-activated mixes in marine environment were investigated and compared to OPC systems. The incorporation of paper sludge ash led to high early strengths, a decrease in the effective porosity of alkali-activated slag concretes and generally a reduced water absorption, and enhanced the performance against chloride ion attack in mixes with freshwater, as well as the resistance of the cements in sulphate attack especially when mixed with seawater. The addition of seawater in the mixes increased the resistance to sulphate attack and the compressive strength in alkali-activated systems, as opposed to OPC concretes in which mixing and curing in seawater had deleterious effects. The study gives promise for the suitability of the tested alkali-activated concrete mixes in seawater environments.

Experimental validation of self-sealing in wellbore cement fractures exposed to high-pressure, CO2-saturated solutions

We present constant-flow experiments of high-pressure CO2-saturated fluid through fracture channels in Portland cement with three different fracture geometries and with three different flow rates. The experiments were conducted in etched cement wafers within a microfluidics device. The evolution of pH was observed optically using phenolphthalein dye and changes in channel volume due to dissolution and/or precipitation were characterized with profilometry and scanning electron microscopy. Abundant precipitation for all three geometries was observed in the low flow-rate experiments, while only dissolution was observed in the high-flow rate experiments. The results bracket self-sealing versus self-opening behavior. The observed functional relationship among flow rate, fracture geometry and aperture in relation to self-sealing is consistent with a diverse set of experiments in the literature conducted under widely varying conditions and with behavior predicted in recent numerical models (Brunet et al., 2016; Cao et al., 2015; Guthrie et al., 2018; Iyer et al., 2017). The results confirm that self-sealing is a quantifiable behavior in ordinary Portland cement systems that is favored at low flow rates and in small-aperture or small hydraulic diameter fracture systems with clear limits imposed by dissolution-dominated conditions of high flow rates.

Towards a further understanding of cement hydration in the presence of triethanolamine

The acting mechanism of triethanolamine (TEA) on cement hydration was studied by combination of techniques including calorimetry, in-situ XRD and pore solution analysis. Results show that, a high dosage of TEA (0.5%) results in accelerated aluminate reaction and retarded silicate reaction during hydration of ordinary Portland cement (OPC). The initial dissolutions of C3S, C3A, C4AF and gypsum are greatly facilitated by TEA. The secondary fast reactions of C4AF and C3A triggered by the earlier sulfate-depletion produce a new exothermic peak before the main hydration peak of C3S that usually presents as a shoulder after the main hydration peak in the reference sample. TEA retards the hydration of pure C3S, but much more severely delays the silicate reaction in OPC system, attributed to the negative interference of aluminate reaction on silicate reaction. The new insights into the interaction between TEA and OPC contribute to the theoretical base for regulating cement hydration.

Durability study of AAMs: Sulfate attack resistance

This paper is a part of works intended to determine more appropriate durability test methods for alkali activated materials (AAMs). Indeed, the current methods used to characterize durability of AAMs are those initially developed for ordinary Portland cement (OPC) and blended OPC. As the chemistry that governs both AAMs and OPC systems is completely different, using OPC durability methods for AAMs could induce inaccurate results. This work aims to study sulfate resistance of alkali activated slag (AAS), alkali activated fly ash (AAFA) and OPC (used as reference) to propose appropriate sulfate resistance test for AAMs by using ASTM C1012 as a basis. Both temperature of curing and sodium sulfate concentration were studied. Expansion of samples was evaluated over time. Results showed that all the OPC bars exceeded the limit compliance with less expansion for those precured at 35 °C. The expansion was attributed in all cases to gypsum and ettringite formation. AAS samples underwent expansion that remains below the limit compliance. At high curing temperature, an initial high expansion attributed to water absorption by the formed porosity was observed. For AAFA systems, no expansion was detected whatever the curing regime and the sulfate concentration, showing a great resistance of such systems to sodium sulfate attack.

Effect of SCMs on the freeze-thaw performance of iron-rich phosphoaluminate cement

Due to the low durability of ordinary Portland cement (OPC), the deterioration of OPC-based materials is very severe in marine structures exposed to cold weather. In contrast, iron-rich phosphoaluminate cement (iron-rich PAC) has good durability and is promising for applications in marine construction. In this context, in the present study, the freeze-thaw (F-T) performance of iron-rich PAC mortar was evaluated and compared with those of OPC and sulphoaluminate cement (SAC) mortars. In addition, the influences of supplementary cementitious materials (SCMs), such as fly ash (FA), limestone powder (LP) and gypsum (GP), on the F-T behaviour of the blended iron-rich PAC mortar were carefully investigated by testing the compressive and flexural strengths, analysing the pore structure using mercury intrusion porosimeter (MIP), and examining the microstructure using XRD and SEM-EDS analysis. The experimental results elucidated that the F-T performance of the iron-rich PAC mortar was far better than those of the OPC mortar and the SAC mortar. In the SCM blended iron-rich PAC systems, the most favourable modification results were obtained with replacement by LP at the optimum dosage of 3–9% (wt%). In this replacement range, the F-T resistances of the LP blended iron-rich PAC systems were better than that of the reference PAC (without SCMs). Further, the F-T performances of the FA and LP blended iron-rich PAC systems were superior to those of the OPC and SAC systems.

Influence of fine cement sand paste in preparation of cementitious materials

The fine cement replacement in conventional cement plays an important role in the microstructure development. To date, no studies have been done to analyze the mixing of fine cement, sand, and water under partial replacement of conventional cement. Therefore, this paper explores the influence of fine cement sand paste on cementitious materials. In this study, the fine calcium sulfoaluminate cement (CSA) cement was prepared to have an average diameter of 2.4 μm. Furthermore, its partial replacement at different percentages was investigated and compared to the ordinary Portland cement (OPC) system. For mortar preparation, a new method is proposed in this paper. First of all, the fine cement, sand, and water are mixed to form a paste and then conventional cement is added. Results emphasized that strength, porosity, permeability, and crack widths in the interfacial transition zone (ITZ) are more affected by this technique. It is concluded that partial replacement of 20% fine CSA content results in improved strength by 30%–35% as compared to the OPC system. Moreover, porosity and permeability were also reduced by 60%–70%. Also, the crack widths at the interfacial transition zone (ITZ) were also reduced up to 60%. This new technique for mortar preparation of fine cement can be applied to form a good microstructure network in cementitious composites.

Elucidating how particle packing controls rheology and strength development of dense cementitious suspensions

Although maximizing particle packing strategy is primarily applied to formulate high performance cementitious suspensions, this may induce constraints for the growth of hydration products, resulting in reduced microstructural evolution at later ages. This paper elucidates the effects of particle packing on rheology and strength development of dense suspensions containing ordinary portland cement (OPC) and supplementary cementitious materials (SCMs). The particle packing was altered through tuning water film thickness to examine its impact over transition of cementitious suspensions from concentrated state to the onset of flow state. This transition was characterized by determining the optimum water demand to achieve maximum solid concentration and minimum water demand to initiate flow. A series of virtual microstructural simulations were also performed to examine the effect of excess water on inter-particle spacing and formation of the connected solid network through formation of main cement hydrate (i.e., calcium-silicate-hydrate (C-S-H)). The results indicate that although transition of the cementitious suspension from concentrated state to the onset of flow state reduces particle packing and elevates separation between neighboring particles, these effects become less pronounced for the OPC-SCM systems than the plain OPC system. The synergistic effect between OPC and SCMs on strength development is controlled by water extent. An account of saturated surface area effect, rate of strength evolution slows down at concentrated state. The outcomes of this study can be applied to optimize the design of dense cementitious suspensions by exploiting optimal particle packing while enabling strength development by providing pore space for growth of hydration compounds.

Characterization on the recycling of waste seashells with Portland cement towards sustainable cementitious materials

This work introduces a cleaner production practice of transforming waste seashells into new minerals for sustainable cementitious materials. Waste seashells were recycled into fine powder through regular crushing and ball-milling processes. Multi-scale studies characterized systematically the reaction mechanisms of waste seashell powder in ordinary Portland cement system. Seashell powder was studied as both a cement replacement and an additional mineral filler, and its roles were explored through workability of fresh cement mixtures, hydration of cement, and mechanical behaviors of hardened cement mixtures. The results indicated that seashell powder enhanced the hydration of cement through its physical and chemical interactions with both cement clinker phases and hydration products. The mechanical strength of hardened cement mixtures was directly improved when the seashell powder was used as an additional filler. Additions of seashell powder, either as a cement replacement or an additional filler, modified the rheological behaviors of fresh cement mixtures. The hydrated CSH matrix phases developed with seashell powder were clearly enriched by the embedded well-dispersed nanosized clusters (with diameter around 5–10 nm). Parallel comparisons between seashell powder and limestone powder confirmed the higher surface properties and chemical reactivities of seashell powder than limestone powder in cement system.