ORCID Profile
0000-0003-3548-2487
Current Organisations
Leipzig University of Applied Sciences
,
Federation University
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Publications
Mechanical Behavior and Frost-Resistance of Alkali-Activated Cement Concrete with Blended Binder at Ambient Curing Condition
Publisher: MDPI AG
Date: 04-02-2021
DOI: 10.3390/BUILDINGS11020052
Abstract: Concrete is the most commonly used construction material because of its various advantages, such as versatility, familiarity, strength, and durability, and it will continue to be in demand far into the future. However, with today’s sensitivity to environmental protection, this material faces unprecedented challenges because of its high greenhouse gas emissions, mainly during cement production. This paper investigates one of the promising cement replacement materials, alkali-activated cement (AAC) concrete. Being produced mainly from byproduct materials and having a comparable structural performance to conventional concrete, AAC concrete can transform the construction industry. Mechanical properties such as compressive and flexural strength and the relationship between them are studied. Different source materials such as fly ash (FA), ground granulated blast furnace slag (GGBS), silica fume (SF), and Metakaolin (MK) are used. The effect of the source materials and the activator solutions on the concrete performance is studied. Furthermore, the freeze-thaw resistance of the concrete is studied. The study results showed that the behavior of AAC depends highly on the source material combinations and type used. The effect of the alkaline solution is also dependent on the source material used. Mixes with higher GGBS content showed the highest strength, while mixes with MK showed the highest flexural strength. The freeze-thaw test results showed that proper design of AAC concrete with lower water content is critical to achieving a good resistance.
Use of maturity method to estimate early age compressive strength of slab in cold weather
Publisher: Wiley
Date: 25-01-2022
Abstract: Accurate estimation of the in situ strength of concrete at early age is very important as it provides the necessary information required to start subsequent construction operations. Overestimation of the strength may cause serious safety hazards and underestimation may lead to unnecessary costly delays. This study investigates the performance of the maturity method in estimating the strength of in situ concrete subjected to cold weather at early age. Instrumented concrete slabs were subjected to cold weather conditions at early ages and their strengths were measured using drilled core s les from the slab. Sensors embedded in the slabs measured the temperature in the concrete which was used to estimate the strength using the maturity method. The measured core strengths at 24 and 72 h after casting are then compared with the estimated strengths using the maturity method and its performance is evaluated. The core strengths are also compared with the strength of standard cylinders cured at the same condition as the slabs. More than 250 cylinders from two slab thicknesses and four batches of concrete were used in the experiments to obtain statistically significant experimental data. The results show that the maturity method performed much better than the standard cylinder strength. On average the standard cylinder strength underestimated the core strength by more than 40% while the maturity method overestimated the strength by less than 10% with a lower variation.
Effect of Wood/Binder Ratio, Slag/Binder Ratio, and Alkaline Dosage on the Compressive Strength of Wood-Geopolymer Composites
Publisher: Springer Nature Switzerland
Date: 2023
Freeze–thaw resistance and sorptivity of fine‐grained alkali‐activated cement concrete
Publisher: Wiley
Date: 10-12-2022
Abstract: The paper investigates the freeze–thaw resistance and sorptivity behavior of fine‐grained alkali‐activated concrete cured at ambient temperature. A blended binder system containing fly ash, ground granulated blast furnace slag, and silica fume was used. A combination of sodium hydroxide and sodium silicate was used as an activator. The freeze–thaw resistance was evaluated based on mass loss (scaling), and the extent of internal damage was assessed by testing the ultrasonic time at different cycles. Initial and secondary sorptivity coefficients were calculated based on the cumulative water absorption values at different time intervals. Alkali content, sodium silicate to sodium hydroxide ratio, and water to binder ratio were investigated. The experimental results showed that water to binder ratio is the most significant parameter for the scaling higher ratios result in higher scaling. In terms of internal damage, alkali content is the most significant. The increase of alkali increased the amount of internal damage in the concrete. The initial sorptivity coefficient increased with the water and alkali content and decreased with the silicate content. The secondary sorptivity coefficient showed no significant change with the investigated parameters.
Bond induced concrete splitting failure in textile-reinforced fine-grained concrete
Publisher: Elsevier BV
Date: 10-2021
Parametric study on bond of GFRP bars in alkali-activated cement concrete
Publisher: Thomas Telford Ltd.
Date: 07-2020
Abstract: Bond behaviour plays an important role in the design and performance of reinforced-concrete structures. In this study, finite-element modelling is used to perform a parametric study. The bond between the glass fibre-reinforced polymer (GFRP) bar and alkali-activated cement concrete is modelled by surface-based cohesive behaviour. The accuracy of the model is validated by comparing model predictions with experimental results. The effect of concrete cover, bar diameter, compressive strength, lead length, embedment length and GFRP elastic modulus on bond behaviour is investigated. Each of these parameters are varied based on a range of applicable values to study their influence on bond behaviour. The parametric study showed that bond behaviour is mainly affected by concrete cover, bar diameter, embedment length and the compressive strength of the concrete. The effect of the elastic modulus of the GFRP bar is not as pronounced as that of the other parameters, while the influence of lead length can be avoided by providing enough unbonded length at the loaded end. The parametric study is further used to calibrate a well-known bond equation and develop a new regression equation for predicting the maximum bond stress. The predicted results from these equations showed a good agreement with the experimental results as well as those of the finite-element model.
Maturity method to estimate early age concrete strength in cold weather: alternative activation energy calibration
Publisher: Informa UK Limited
Date: 28-07-2022
Bond behaviour of GFRP reinforced geopolymer cement concrete
Publisher: EDP Sciences
Date: 2017
Review and Experimental Investigation of Retarder for Alkali-Activated Cement
Publisher: Springer International Publishing
Date: 2023
Rheology of Alkali-Activated Blended Binder Mixtures
Publisher: MDPI AG
Date: 18-09-2021
DOI: 10.3390/MA14185405
Abstract: Alkali-activated cement (AAC) is an alternative cement that has been increasingly studied over the past decades mainly because of its environmental benefits. However, most studies are on heat-cured AACs and are focused on mechanical properties. There is a lack of research on the fresh properties of ambient-cured AAC systems. This study investigates the rheological properties of ambient-temperature-cured alkali-activated blended binder mixtures activated with sodium silicate and sodium hydroxide solutions. The influence of binder amount, alkaline solid to binder ratio (AS/B), sodium silicate to sodium hydroxide solids ratio (SS/SH), and total water content to total solid (from the binding materials) ratio (TW/TS) on the rheological properties are investigated. The effect of borax as an admixture and silica fume as a replacement for fly ash is also investigated. The results showed that both the yield stress and plastic viscosity are mainly affected by the binder content and TW/TS ratio decreasing with the increase of each parameter. The yield stress increased with the increase of the SS/SH ratio. Borax significantly reduced the yield stress, while silica fume’s effect was dependent on its dosage.
SHRINKAGE OF ALKALI-ACTIVATED BLENDED BINDER MIXTURES
Publisher: ISEC Press
Date: 07-2022
DOI: 10.14455/ISEC.2022.9(1).AAC-05
Abstract: Alkali-activated cement (AAC) has excellent mechanical and durability properties. Most of all, AAC is environmentally friendly and utilizes less raw material than ordinary Portland cement (OPC). It has been 60 years since the initial appearance of AAC in the research world. Since then, the knowledge has matured from the various research conducted in the area. Studies have shown that the shrinkage of AAC is relatively large compared to OPC, making it susceptible to cracking. For AAC to be an ideal replacement for OPC, its shrinkage behavior and factors affecting it need to be investigated in detail. This paper studies the effect of alkaline solid to binder ratio (AS/B), sodium silicate to sodium hydroxide solids ratio (SS/SH), and total water to total solid binder ratio (TW/TS) on the shrinkage. The results showed that TW/TS is the main factor affecting the shrinkage of AAC. An increase in TW/TS reduced the shrinkage significantly. AS/B also reduced the shrinkage but at a lower significance. SS/SH ratio showed no significant effect. Such understandings of the different factors affecting the shrinkage of AAC can help design a mixture with a better shrinkage behavior.
Setting Time and Strength Monitoring of Alkali-Activated Cement Mixtures by Ultrasonic Testing
Publisher: MDPI AG
Date: 10-04-2021
DOI: 10.3390/MA14081889
Abstract: Alkali-activated cement (AAC) is a promising binder that replaces ordinary Portland cement (OPC). In this study, the development of setting time and strength of AAC mixes were studied using ultrasonic testing method. The test results were compared with traditional Vicat setting time and compressive and flexural strengths. The findings showed that setting times and strengths have a strong correlation with ultrasonic velocity curve. The initial setting time corresponds well with the ultrasonic velocity curve’s dormant period, and the final setting time with the time it takes to reach the velocity curve’s maximum acceleration. Both setting times also showed a correlation with the value of the maximum acceleration. An exponential relation was found between the ultrasonic velocity and the compressive and flexural strengths. The effect of binder content, alkaline solid to binder ratio (AS/B), sodium silicate to sodium hydroxide solids ratio (SS/SH), and total water to total solid binder ratio (TW/TS) on the strength and setting time are also studied using Taguchi method of experimental design. AS/B ratio showed a significant influence on the setting time of AAC while TW/TS ratio showed only a minor effect. The ultrasonic velocities were able to capture the effect of the different parameters similar to the compressive strength. The velocity decreased mainly with the increase of TW/TS ratio and binder content, while AS/B and SS/SH ratios showed a lower influence.
Alkali activated cement mixture at ambient curing: Strength, workability, and setting time
Publisher: Wiley
Date: 28-10-2021
Abstract: The success of ordinary Portland cement (OPC) comes at a risk to the environment because of the large carbon dioxide emissions associated with cement manufacturing. This has led the scientific community to look for alternative cementitious materials with lower environmental impact. Alkali activated cement (AAC) is an excellent alternative to this end. In this study, the effect of binder content, alkaline solid to binder ratio (AS/B), sodium silicate to sodium hydroxide solids ratio (SS/SH), and total water content to total solid binder ratio (TW/TB) on the strength, setting time and flowability of ambient cured AAC mixtures are studied using Taguchi method of experimental design. Binder content was varied from 550 to 750 kg/m 3 , AS/B ratio from 0.14 to 0.22, SS/SH ratio from 1.5 to 2.5, and TW/TB ratio from 0.29 to 0.39. The study results showed that within the investigated range, an increase in binder content has a minor effect on strength but resulted in a considerable increase in setting time and flowability. An increase in the AS/B ratio resulted in increased flowability and setting time and a decrease in strength. Moreover, the study also investigated the relationship between compressive strength and flexural strength.
Bond behaviour of GFRP reinforcement in alkali activated cement concrete
Publisher: Elsevier BV
Date: 11-2017
Effect of Corrosion on the Bond Behavior of Steel-Reinforced, Alkali-Activated Slag Concrete
Publisher: MDPI AG
Date: 11-03-2023
DOI: 10.3390/MA16062262
Abstract: Alkali-activated slag concrete (ASC) is regarded as one of the most promising sustainable construction materials for replacing ordinary Portland cement concrete (OPC) due to its comparable strength and outstanding durability in challenging environments. In this study, the corrosion of steel bars embedded in ASC and OPC was studied by means of an electrically accelerated corrosion test of steel bars in concrete. Meanwhile, the bond performance of the corroded steel bars embedded in ASC was tested and compared with corresponding OPC groups. The results showed that ASC and OPC behaved differently in terms of bond deterioration. The high chemical resistance of ASC decreased the corrosion of steel bars and, thus, increased the residue bond strength and the bond stiffness.
Bond of spliced GFRP reinforcement bars in alkali activated cement concrete
Publisher: Elsevier BV
Date: 09-2017
A Method for the Design of Concrete with Combined Steel and Basalt Fiber
Publisher: MDPI AG
Date: 23-09-2021
DOI: 10.3390/APP11198850
Abstract: Combining different fiber types may improve the mechanical properties of fiber reinforced concrete. The present study is focused on investigating hybrid fiber reinforced concrete (HFRC) with steel and basalt fiber. Mechanical properties of fiber reinforced fine-grained concrete are investigated. The results demonstrate that using optimal steel and basalt fiber reinforcement ratios avoids concrete mixtures’ segregation and improves their homogeneity. Concrete with hybrid steel and basalt fiber reinforcement has higher strength. Effective methodology for proper design of HFRC compositions was proposed. It is based on the mathematical experiments planning method. The proposed method enables optimal mix proportioning of high-strength fine-grained concrete with hybrid steel and basalt fiber reinforcement.
Bond Properties of Sand-Coated GFRP Bars with Fly Ash–Based Geopolymer Concrete
Publisher: American Society of Civil Engineers (ASCE)
Date: 10-2016
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