Alkali-activated Cement Mortars Research Articles

Effect of superplasticizer in geopolymer and alkali-activated cement mortar/concrete: A review

Abstract The cement and construction industry creates around 10% of the global carbon footprint. Geopolymer and alkali-activated concrete provide a sustainable solution to conventional concrete. Due to its disadvantages, the practical usage of geopolymer and alkali-activated concrete is limited. Workability is one of the issues faced in developing geopolymer and alkali-activated concretes. Plenty of research was conducted to provide a solution to enhance the ability to use different superplasticizers (SPs). The present article extensively reviews the effects of SPs on geopolymer and alkali-activated concretes. The research articles published in the last 5 years in high-quality journals are considered for the chemical composition of the different SPs and analyses of their exact impact on geopolymer and alkali-activated cement mortar and concrete. Later, the impact of SPs on the normal consistency and setting times of cement mortar, workability, compressive strength, flexural strength, split tensile strength, microstructure, and water absorption of geopolymer and alkali-activated concrete was determined. SPs improve the geopolymer and alkali-activated concretes upon their use in desired dosages; more dosage leads to negative effects. Therefore, selecting the optimal superplasticizer is essential since it impacts the performance of the geopolymer and alkali-activated concrete.

Creep of alkali-activated cement mixtures

Alkali activated Cement (AAC) is one of the alternatives to ordinary portland cement (OPC) and recently attracted a lot of attention due to its environmental benefits as a sustainable construction material for building and infrastructures. However, one area of significance is related to long-term durability, especially in time-dependent deformation such as shrinkage and creep. The previous results of shrinkage tests of AACs validated the importance of curing temperature and creep in the volumetric stability of AACs. Thus, this work measured creep characteristics of four different AAC mortar cylinders over 20 months. The results were compared with the predicted creep values for ordinary portland cement mixtures calculated according to the ACI 209 method. The creep coefficient of fly ash-rich and slag-rich mixtures after 20 months of loading was about 2 and 4 times, respectively, larger than the predicted coefficient for portland cement mixtures. By applying nonlinear least squares estimation, a reliable equation (with R2 > 96%) was proposed to predict the viscous response of each studied AAC mortar. The findings of this paper signified that slag-rich mixtures were much more prone to viscoelastic deformation under constant load, which resulted in larger drying shrinkage under internal drying stresses—as such, increasing the slag content in AACs led to a larger time-dependent (viscous) response. Additionally, it was observed that high curing temperature changed the creep response (different variables in the estimated equation), increased the maturity, and lowered the viscous response of AACs.

Drying shrinkage behavior of hybrid alkali activated cement (HAAC) mortars

Shrinkage is a vital factor for hybrid alkali activated cement (HAAC) related to durability. In this work, the drying shrinkage behavior of HAAC mortars with various precursors, curing regimes and activator states was investigated. Portland cement mortar and alkali activated cement (AAC) mortar were used as control groups. Results showed that the drying shrinkage magnitude of HAAC mortar is lower than that of AAC mortar but higher than that of Portland cement mortar. Slag-based HAAC mortar shows the largest shrinkage value and the introduction of fly ash could temper shrinkage slightly. The steam curing and solid activation could mitigate the magnitude of drying shrinkage for HAAC mortar. The drying shrinkage is irrespective of the water loss in this study. MIP, SEM, and XRD analyses were undertaken to gain more insights into the mechanisms of drying shrinkage of HAAC. More crystalline phase and higher Ca/Si gel of HAAC paste tempers the drying shrinkage of HAAC mortar. The larger capillary pores size is likely to explain the lower shrinkage of fly ash-based HAAC mortar.

An innovative way to enhance the high temperature properties of alkali activated cement mortars prepared by using glass powder as precursor

An innovative way to enhance the high temperature properties of alkali activated cement mortars prepared by using glass powder as precursor

Reaction mechanisms of alkali-activated glass powder-ggbs-CAC composites

This paper discusses the alkali activation reaction and the alkali-silica reaction (ASR) of the alkali activated cement (AAC) using glass powder (GP) as the major precursor and glass cullet (GC) as the fine aggregate. For the AAC, the proportion of GP was fixed at 75% by weight and different dosages of ground granulated blast furnace slag (GGBS) and calcium aluminate cement (CAC) were incorporated. The main reaction product of the alkali-activated glass powder and slag was an amorphous gel N-(C)-A-S-H according to scanning electron microscopy (SEM)-back scattered electron (BSE) result. New crystalline phases including zeolite and katoite were detected by X-ray diffraction (XRD) in the AAC pastes after the incorporation of CAC in addition to the N-(C)-A-S-H gel. The compressive strength of the AAC mortar was increased with the increase of CAC dosage when the CAC content was lower than 10%. But further increase of the CAC content decreased the strength of the alkali-activated mortar due to the formation of zeolite and katoite loosening the microstructures. The alkali-activated glass/slag cement suffered from severe expansions due to ASR and the expansion exceeded 1000 micro strain after 14 days of alkaline immersion. The addition of CAC significantly decreased the ASR expansion.

ASR expansion of alkali-activated cement glass aggregate mortars

Previous studies showed using calcium aluminate cement (CAC) can effectively mitigate the alkali-silica reaction (ASR) expansion of alkali-activated cement (AAC) mortars incorporating glass cullet (GC) as fine aggregates but the mechanism was not clear. This study presents a systematic study on exploring the underlying mechanism to fill in the knowledge gap and to ascertain the safe use of GC in AAC to maximize the possibility of recycling of waste glass in construction materials. The results showed that the ASR expansion of alkali-activated glass mortars was more than 1000 με after 1 day of alkaline immersion when using glass cullet as fine aggregates. The incorporation of CAC could decrease the expansion to less than 1000 με even after 14 days of alkaline immersion. The ASR expansion decreased with the increase of CAC content up to 20%. That was due to several reasons. Firstly, aluminum (Al) in CAC was incorporated in the AAC matrix with tetrahedral and octahedral units. The tetrahedral unit increased with the increase of CAC content, which required more Na ions to balance the excessive charge. Therefore, the alkalinity of the pore solution decreased and the ASR expansion decreased consequently. Besides, more AAC gel was formed due to the CAC incorporation, which decreased the alkalinity of the pore solution as well. But further increase the CAC content (25%) increased the ASR expansion, which might be due to the formation of zeolite that decreased the strength of AAC mortars.

Optimizing the use of recycled glass materials in alkali activated cement (AAC) based mortars

The management of waste glass generated mainly from waste glass beverage bottles has become a pressuring waste management problem. This study presents a novel way to incorporate recycled glass materials into alkali-activated cement (AAC) based pastes/mortars. Waste glass cullet (GC) was used to replace natural aggregates and waste glass powder (GP) was used to partially replace conventional precursors such as ground blast furnace slag (GGBS). Optimization was conducted innovatively aiming at maximizing the total waste glass content in the AAC materials while maintaining adequate mechanical, durability and functional properties of the final products that contained more than 70% of recycled glass materials by mass. Using the developed technology, recycled glass incorporated alkali activated cement based mortars (AAMs) with a 28-day compressive strength of about 40 MPa can be produced. Furthermore, the excellent high temperature resistance of the optimized AAC mortar mixture allowed the retention of over 50% of the original strength after 2 h of exposure at 800 °C. The experimental results also showed that the detrimental expansion caused by the alkali silica reaction (ASR) between the alkali and the waste GC in the AAC mortars could be controlled successfully by using additional aluminium sources such as calcium aluminate cement (CAC). Further reduction in ASR expansion was possible via adjusting the GC to binder ratio. Also, the drying shrinkage level could be controlled to less than 1000με which is a significant improvement to conventional AAC materials prepared by using GGBS. The findings presented in this paper are pivotal for maximizing the recycling and reusing of waste glass in AAC.

A ternary optimization of alkali-activated cement mortars incorporating glass powder, slag and calcium aluminate cement

This paper introduces the use of a simplex-centroid design method, together with a ternary contour diagram, to evaluate the effect of blending different proportions of soda lime glass powder (GP), ground granulated blast furnace slag (GGBS) and calcium aluminate cement (CAC) on the compressive strength, alkali-silica reaction (ASR) expansion, drying shrinkage and high temperature resistance of alkali-activated cement (AAC) mortars prepared with the use of crushed glass cullet (GC) as aggregates. The relationship between performance of the geopolymer and precursor composition was established. It was found the ASR expansion increased with the increase of GP content and the addition of CAC as the replacement of GGBS could significantly reduce the ASR expansion. The drying shrinkage increased with the increase of GGBS contents. The residual strength coefficient of the mortars after high temperature exposure increased with the increase of CAC content and could be higher than 100%. And the strength coefficient increased with the increase of GP content resulted from its partial melting at the high temperature. It was found that the GP content should be in the range of 77–90%, the GGBS content should be lower than 5% and the CAC content should be higher than 10% to achieve acceptable ASR expansion and drying shrinkage.

Gamma and neutron attenuation properties of alkali-activated cement mortars

Radiation-shielding properties of alkali-activated cement (AAC) mortar mixtures prepared using different precursors such as ground granulated blast furnace slag (GGBFS), fly ash (FA), metakaolin (MK) and waste clay material containing boron (WCB) were investigated comparatively with Ordinary Portland Cement (OPC) mixture. The gamma linear attenuation coefficients of the mixtures were determined both experimentally and theoretically. The experimental coefficients of the mixtures were measured with NaI(Tl) detection system for gamma energies of 137Cs (662 keV) and 60Co (1173 and 1332 keV) and the gamma transmission parameters (half-value layer, HVL; tenth-value layer, TVL and mean free path, MFP) were determined using these coefficient values. The theoretical coefficients of the mixtures were calculated using XCOM software for the energy range of 10–3000 keV. In addition, neutron attenuation coefficients of the mortar mixtures were theoretically calculated with the NCNR computation software for thermal (0.025–1 eV), slow (1–10 eV), resonance (10–300 eV), intermediate (300 eV-1 MeV) and the fast neutrons (1 MeV–20 MeV). Test results indicated that GGBFS and FA based alkali-activated cement mortars had similar gamma attenuation properties to the OPC mortar while the WCB and MK-incorporating AAC mixtures had slightly worse properties in this respect. In terms of thermal and slow neutron shielding properties only AAC mixtures containing WCB showed significantly better behaviour compared to OPC. For neutrons having higher energy levels than slow neutrons, all AAC and OPC mortar mixtures showed comparable properties.

Strength prediction and mix design procedures for geopolymer and alkali-activated cement mortars comprising a wide range of environmentally responsible binder systems

ABSTRACTThis research presents a mix design methodology for geopolymer (GP) and alkali activated (AA) mortars based on metakaolin and industrial waste products activated using potassium silicate. The aim is to enable a wide range of mix designs to be specified to given compressive strength, consistency and environmental footprints to facilitate their adoption as a Portland cement (PC) alternatives in the construction industry in applications such as fibre-reinforced building cladding systems. The impact of the work is timely as literature quantifying the effects of mix parameters on broad families of GP and AA materials are limited, and no standardized performance-based methodology exists. Initially, effects of binder composition on mechanical and environmental properties are presented for a standard GP mix design using contoured ternary plots for a range of material blends. Next, effects of altering mixture parameters such as liquid/solid, silica/alumina and activator/binder ratios are quantified for three selected binder compositions before a preliminary mix design methodology is presented allowing initial selection of mixture proportions. Finally, correlation analysis is used to identify multiple mix variables strongly correlating with strength, and regression modeling used to present predictive tools with average errors <6%.

The efficiency of plasticizing surfactants in alkali-activated cement mortars and concretes

Functionality of mortar and concrete mixes is regulated by surfactants, which act as plasticizers. The molecular structure of these admixtures can be changed during hydration of alkali-activated cements (AAC). The objective was to determine the chemical nature of plasticizers effective for property modification of mortars and concretes based on AACs with changing content of granulated blast furnace slag from 0 to 100 %. The admixtures without ester links become more effective than polyesters when content of alkaline component increase. The admixtures effective in high alkaline medium were used in dry mixes for anchoring (consistency of mortar 150 mm by Vicat cone; 1 d tensile strength in bending / compressive strength of mortar 6.6 /30.6 MPa) and in ready-mixed concretes (consistency class changed from S1 to S3, S4 with consistency safety during 60 min; 3 d compressive strength of modified concrete was not less than the reference one without admixtures).

Use of waste glass in alkali activated cement mortar

This paper presents a study on alkali activated cement (AAC) mortar produced with waste soda-lime-silica glass. The waste glass was used simultaneously as a precursor and fine aggregates in the alkali activated fly ash-slag mortar. The influences of waste glass in cullet and powder forms on workability, compressive and flexural strengths, fire resistance of the AAC mortar were investigated. The experimental results showed that the workability was gradually increased as the replacement level of natural sand by glass cullet was increased, and it was significantly improved with decreasing aggregates-to-binder ratios. The mechanical properties data indicated that the compressive strength was reduced as the glass cullet content increased. However, for the flexural strength, the optimum percentage of glass cullet replacement was 50%. Due to the low reactivity, a reduction in strength was observed when the glass powder was used to replace the fly ash and slag. Nevertheless, in terms of fire resistance, the incorporation of glass cullet could improve the resistance of the AAC to high temperature exposures (800 °C). In particular, the AAC mortar prepared with the glass powder as a precursor exhibited remarkable resistance to high temperature. The use of waste glass in AAC material was feasible from the mechanical properties and fire resistance points of view.

China clay waste as aggregate in alkali-activated cement mortars

Every 1 t of china clay produced in the UK generates 9 t of waste material. A limited quantity of the coarser waste has beneficial use as a building stone or secondary aggregate in concrete and asphalt, but there are currently limited uses for the finest waste fraction. ‘Mica’ waste is a mixture of fine minerals and is one of the forms of waste with little beneficial use other than the restoration of old quarries. With an aim to find new commercially viable and low environmental impact uses in construction, this paper focuses on the use of china clay waste as an aggregate in alkali-activated cement mortar. Based on preliminary analysis of the compressive strength of binders using slag and fly ash, optimum binders were selected to produce mortars using mica and other forms of china clay waste as aggregate. The mortars were then compared in compression with control specimens using standard sand. Although the results show that the test mortars were generally weaker than the control samples, the paper concludes there are opportunities for their use.

도로포장 보수재 활용 가능성 평가를 위한 알칼리 활성 시멘트 모르타르 기초연구

PURPOSES : This study is to evaluate the feasibility of using the alkali activated cement concrete for application of partial-depth repair in pavement. METHODS : This study analyzes the compressive strength of alkali activated cement mortar based on the changes in the amount/type/composition of binder(portland cement, fly ash, slag) and activator(NaOH, <TEX>$Na_2SiO_3$</TEX>, <TEX>$Na_2CO_3$</TEX>, <TEX>$Na_2SO_4$</TEX>). The mixture design is divided in case I of adding one kind-activator and case II of adding two kind-activators. RESULTS : The results of case I show that <TEX>$Na_2SO_4$</TEX> based mixture has superior the long-term strength when compared to other mixtures, and that <TEX>$Na_2CO_3$</TEX> based mixture has superior the early strength when compared to other mixtures. But the mixtures of case I is difficult to apply in the material for early-opening-to-traffic, because the strength of all mixtures isn't meet the criterion of traffic-opening. The results of case II show that NaOH-<TEX>$Na_2SiO_3$</TEX> based mixtures has superior the early/long-term strength when compared to NaOH-<TEX>$Na_2SiO_3$</TEX> based mixtures. In particular, the NaOH-<TEX>$Na_2SiO_3$</TEX> based some mixtures turned out to pass the reference strength(1-day) of 21MPa as required for traffic-opening. CONCLUSIONS : With these results, it could be concluded that NaOH-<TEX>$Na_2SiO_3$</TEX> based mixtures can be used as the material of pavement repair.

A ternary optimisation of mineral additives of alkali activated cement mortars

The effects of binary and ternary combinations of ground granulated blast furnace slag (GGBFS), fly ash (FA) and silica fume (SF) on compressive strength, flexural strength, water sorptivity, permeable voids and drying shrinkage of steam cured alkali-activated cement (AAC) mortars were investigated within the scope of this study. Also, three-level full factorial experimental design and response surface method were used for the optimisation of the amount of mineral additives by maximising compressive and flexural strengths while minimising drying shrinkage, water sorptivity and permeable voids. The use of ternary blends in AAC provided significant decreases in drying shrinkage, water sorptivity and permeable void content. However, the mechanical performance of ternary blended AAC has been negatively affected compared to GGBFS mortar. Nevertheless, compressive strength values of all binary and ternary blends of AAC were higher than conventional Portland cement mortar. The optimum AAC composition was obtained with a ternary mixture containing 20.3% FA, 18.9% SF and 60.8% GGBFS.

바텀애쉬를 결합재로 사용한 알칼리 활성화 시멘트 모르타르의 최적배합에 관한 연구

이 연구에서는 알칼리 활성화 시멘트 모르타르에 대한 결합재로서 바텀애쉬의 적용성을 평가하였으며, 배합 구성에 따른 재료 특성 변화를 파악하기 위한 실험을 수행하였다. 바텀애쉬를 사용한 알칼리 활성화 시멘트 모르타르 실험에서는 물/바텀애쉬 비, 활성화제/바텀애쉬의 비, 수산화나트륨에 대한 규산나트륨의 비, 양생 온도, 바텀애쉬의 분말도를 주된 실험 변수로 하여 유동성과 강도 실험을 수행하였다. 그 결과, 60oC 고온 양생을 할 경우에는 적절한 유동성과 함께 40 MPa 이상의 압축강도를 얻을 수 있음을 확인하였으며, 20℃ 상온 양생 시에도 초기 강도 발현은 매우 느리지만 재령 28일 강도 30 MPa 정도가 발현되었다. 또한 실험 결과로부터 바텀애쉬를 사용한 알칼리 활성화 시멘트 모르타르의 적정 최적 배합 범위를 도출하였으며, 이와 함께 실험 결과를 바탕으로 인공신경망 분석법을 적용하여 배합 구성 변화에 따른 유동성 및 압축강도의 변화를 예측하였다.

Automated identification of the aggregate–paste interfacial transition zone in mortars of silica sand with Portland or alkali-activated slag cement paste

The interfacial transition zone (ITZ) between cement paste and aggregate strongly influences the mechanical and transport properties of mortar and concrete. Backscattered electron (BSE) imaging in the scanning electron allows anhydrous cement, hydration products, and porosity in this region to be quantified by compositional contrast. When the aggregate has a similar brightness to the hydrates, as in some alkali-activated cement mortars with silica sand, automated identification of the aggregate edge in the BSE image is difficult. Manual identification is laborious and prone to errors. Here we demonstrate use of energy dispersive X-ray (EDX) dot maps, acquired concurrently with the BSE to enable compositional identification of the aggregate edge automatically. The mortars studied were prepared with OPC or slag activated with either sodium silicate or potassium hydroxide. The edges of the silica sand aggregate particles were located to within 2.5 μm, and the gradation of microstructure across the ITZ was quantified automatically. Hydrates were found most successfully to infill the ITZ in sodium silicate-activated slag cement mortars.