Effect of Tidal Zone and Seawater Attack on Alkali- Activated Blended Slag Pastes

Gharieb M., Mosleh Y.A., Rashad A.M.

This article outlines the contribution of various precursors named ground-granulated blast furnace slag (slag) and metakaolin (MK) as a binary blend (s70m30) as well as slag, MK and fly ash (FA) as...

Rashad A.M., Morsi W.M., Khafaga S.A.

The use of limestone powder (LSP) as a cement replacement is used in abundant applications due to its low cost and wide availability. Adversely, the use of LSP as a part of the precursors of alkali-activated materials (AAMs) is still in the developing stage. This scarcity of studies opened the door and encouraged the researchers for more investigations. Thus, this paper studied the effect of various amounts of LSP on some properties of alkali-activated slag (AAS) pastes activated with NaOH and Na2SiO3 solution. Slag was partially replaced with LSP at ratios of 15–60 wt%. The effects of LSP on mechanical strength, water absorption, chloride penetration permeability, drying shrinkage were studied. Advanced apparatuses were applied to detect the changes in crystalline phases, hydration products and microstructure of the pastes with and without the inclusion of LSP. The results confirmed that 15% LSP was the optimum amount, which is responsible for the highest mechanical strength, lowest water absorption and lowest charge passed. The drying shrinkage was mitigated with the inclusion of LSP. The inclusion of 15% LSP enhanced the 28-day compressive strength and flexural strength by 11.41% and 13.7%, respectively, while the water absorption, charge passed and drying shrinkage were decreased.

Karim M.R., Hossain M.M., Manjur A Elahi M., Mohd Zain M.F.

This study has investigated the strength development of alkali-activated binders (AAB) fabricated from slag, fly ash (FA), rice husk ash (RHA), and palm oil fuel ash (POFA). Materials being used as singular, binary and ternary compositions while Ca(OH)2, KOH and NaOH were used separately as a chemical activator. All the test results of AAB for 10 numbers of different mixes have been compared to ordinary Portland cement (OPC) mortar. Test result reveals that compressive strength of slag activated mortar with 5% NaOH (by weight of binder) achieves 88.2% compressive strength of OPC at 28 days. Among the 10 mixes, AAB4 containing 40% slag, 30% POFA and 30% RHA with 5% NaOH shows a significant compressive strength of 41.7 MPa at 28 days. Flexural strength of alkali-activated mortar with 5% NaOH seems to be acceptable compared with that of OPC mortar at 28 days. It is clearly observed that the strength development of AAB-mortar is greatly influenced by the types and fineness of materials and blending of materials. In contrast, the compressive strength of AAB-mortar is comparatively less influenced by employing different curing methods like water, wetted jute bag and air curing.

Dong M., Elchalakani M., Karrech A.

AbstractThis study compared the effect of seven common curing conditions on the compressive strength, pore alkalinity, efflorescence, and shrinkage of five alkali-activated fly ash and slag (AAFS) ...

Aygörmez Y., Canpolat O., Al-mashhadani M.M., Uysal M.

In this study, metakaolin-based geopolymer samples produced by substitution of silica fume and colemanite waste up to 20% were subjected to high-temperature effects at 300, 600, 900 °C, the wetting-drying effect of 5, 15 and 25 cycles and freezing-thawing effect of 56 and 300 cycles. At the end of the tests, compressive and flexural strengths, ultrasonic pulse velocity and weight changes’ results were examined. In addition to these, micro-computed tomography (CT), XRD and SEM analyses were performed to examine the microstructure properties as well as visual inspection. 5 series produced for high temperature and wetting-drying effects were also produced with polypropylene fiber. It has been observed that samples exposed to 900 °C maintained their stability. Polypropylene fiber has been shown to increase the samples’ flexural strength results compared to the non-fiber samples after exposing to high temperatures. For the freezing-thawing effect, air-entraining admixture was added to 5 series. An increase for compressive strength was seen after 56 cycles but a decrease was seen after 300 cycles. The geopolymer samples thus began to suffer the real distortion effect in subsequent cycles after the freezing-thawing effect, which contributed to geopolimerization in a sense occurring in the first 56 cycles. During the wetting-drying cycles, fluctuations were observed in the results and an increase in the compressive strength, UPV and weight changes’ results after 5 cycles, a decrease in the results after 15 cycles and an increase again in the results after 25 cycles were seen.

Li X., Rao F., Song S., Ma Q.

Few studies have focused on the effect of mineral composition on the mechanical behaviour and evolution of a geopolymer binder in artificial seawater environment. In this study, a geothermal clay-b...

El-Hassan H., Elkholy S.

AbstractThis paper investigates the performance of steel fiber–reinforced alkali-activated slag concrete incorporating different fly ash replacement percentages. Three different molarities of sodiu...

Li X., Rao F., Song S., Ma Q.

In this research, metakaolin-based geopolymers were synthesized to study their deterioration in marine environment. The geopolymers were exposed in air, seawater, dry-wet and heat-cool cycles of seawater for 30, 60 and 90 days. The mechanical property of the geopolymers was characterized through compressive strength measurements, and their microstructures were measured by X-ray diffraction (XRD), scanning electron microscope (SEM) and nuclear magnetic resonance (NMR) apparatus. It was found that seawater environment inhibited the geopolymerization reactions, so that a low amount of tetrahedral silicon of Q4(4Al), Q4(3Al) and Q4(2Al) were formed.

Rashad A.M., Ezzat M.

This research is the first attempt to study the possibility of employing magnetic water (MW), Zamzam water (ZW) and seawater (SW) as mixing water for alkali-activated slag (AAS) pastes. The results of workability, pH value, compressive strength and microstructure of different specimens mixed with each type of water were compared with those mixed with tap water (TW). The X-ray diffraction (XRD), thermogravimetric analysis (TGA) and scanning electron microscopy (SEM) were used to analyze the results. The results showed that using MW, ZW or SW increased the workability, pH value and compressive strength of AAS pastes. The microstructures of the samples prepared with these water types were modified as confirmed by SEM, whilst the polymerization processes were accelerated as confirmed by TGA. It was found that MW has the height improvement followed by ZW and SW, respectively, whilst TW came in the last place.

Gopalakrishnan R., Chinnaraju K.

The durability of a concrete depends upon resistance against various properties like sulfate, chloride, and acid, corrosion environment. One of the important durability properties of the concrete is its resistance against sulfate environment. This research paper outcomes the results of an experimental investigation on durability of geopolymer concrete produced with GBFS (Granulated Blast Furnace Slag), Fly ash (Class F – Grade) and alkaline activators under ambient temperature, subjected to magnesium sulphate and sodium sulphate environment. GBFS was partially replaced by fly ash at various replacement levels from 0 to 50% with a constant concentration of 12 M alkaline activator solution. The main parameters of this study are evaluation of change in weight, strength, and micro structural changes. The techniques used to study the degradation a Scanning Electron Microscopy and X-ray Diffraction methods. Fourier transform infrared spectroscopy was also used as an additional method of study. Geopolymer concrete with GBFS under ambient curing shows better results when compared to geopolymer concrete with GBFS blended with fly ash. In the magnesium sulfate environment, the rate of reduction of strength of GPC with GBFS is 35%, while for 40% replacement of fly ash to GBFS performs well with a strength gain of 10%. Similar observations are also observed in sodium sulfate environment in which 40% replacement of fly ash to GBFS performs well. Therefore, it is concluded that partial replacement 40% of fly ash to GBFS is the appropriate level satisfying the durability properties for ambient cured geopolymer concrete.

Cheah C.B., Tan L.E., Ramli M.

Highly concentrated and corrosive alkaline activators are often used for activating polycondensation reactions of aluminosilicate minerals in geopolymers at elevated temperatures. This study investigated the interaction between Pulverised Fuel Ash (PFA), Ground Granulated Blast Furnace Slag (GGBS) and Silica Fume (SF) activated with small dosages of low alkalinity sodium carbonate and sodium silicate. Tests were inclusive of assessments on the consistency and setting behaviours, mechanical strengths and microstructure properties. Results were compared with Ordinary Portland Cement (OPC) mortars and sodium hydroxide activated geopolymer mortars which were established through an existing study. The mechanical strength of sodium carbonate activated geopolymer was found to be comparable with that of the sodium hydroxide activated geopolymer. Geopolymer mortars with 4% of silica fume exhibited the highest mechanical strength. The sodium carbonate activated binder system comprised largely of an interconnected calcium carbonate crystals framework and C-A-S H gels.

G I., Singh B., Deshwal S., Bhattacharyya S.K.

Reactions between the fly ash/slag composite mix and the Na2CO3/Na2SiO3 activator were monitored through Isothermal conduction calorimetry. The resulting products were analyzed with the help of XRF, XRD and FT-IR techniques. In calorimetric response, the composite pastes had more total heat release than the fly ash paste requiring ∼50% less activation energy to yield reaction products. These products were largely amorphous as observed in the XRD patterns. Rheological studies indicated that composite pastes were very stiff above 25 wt% slag addition as its yield stress was almost doubled to fly ash paste. The compressive strength of hardened pastes increased with increasing slag content and activator dosage and decreased with increasing water-binder ratio. The deposition of reaction products onto the fly ash/slag particle surfaces and also the dense microstructures as observed in FESEM supported higher strength of geopolymer pastes at higher activator and slag contents. The developed paste with standard sand at 1:2 ratio produced mortar with a compressive strength of ∼72 MPa.

Rashad A.M.

Geopolymer is an innovative material and a real alternative to traditional Portland cement for use in the construction industry. Incorporation of the use of geopolymers in civil engineering is one of the most-promising options for reducing environmental impact and the huge energy consumption of Portland cement manufacture. Since geopolymers were discovered, further development has produced more modified, strong, durable and sustainable binders. One option to develop and modify some properties of this system is to add other prospective materials such as nanoparticles. In general, the applications and advances of nanotechnology in geopolymer materials remain limited in comparison with those of traditional cementitious materials. However, in the last few years, the effect of nanoparticles on the properties of geopolymers has been given increased attention. This article presents an overview of earlier studies focused on adding different types of nanoparticles, such as nano-silicone dioxide (SiO2), nano-titanium dioxide (TiO2), nano-aluminium oxide (Al2O3), nano-clay and geothermal nanosilica waste, into different geopolymer matrices. Fresh and hardened properties have been reviewed and briefed. The current review can be used as a guide to know what has already been covered in the research and what should be covered in future studies.

Rashad A.M.

Zuquan J., Xia Z., Tiejun Z., Jianqing L.

Transport of chloride ion into concrete can induce depassivation of reinforcement, which seriously threatens the durability of concrete subjected to marine environment. In this paper, the chloride ion transport and binding capacity of different concrete samples located in marine atmosphere zone, splash zone, tidal zone and submerged zone for 9 and 13 months were tested. And the chloride ion profiles of one whole concrete sample exposed to all the corrosion zones for 13 months was also detected. The effect of fly ash and ground granulated blast furnace slag (GGBS) on the chloride ion transport and binding capacity of all the concrete samples were studied and the optimized replacement ratios of mineral admixtures in marine environment was proposed. The contents of Ca(OH)2 and Friedel’s salt in paste exposed to different corrosion zones were also tested by XRD and DSC-TG. Results showed chloride ion content in separate concrete samples exposed to splash zone and atmosphere zone were lower than that of the other zones, but the opposite results were observed for one whole concrete sample throughout all the corrosion zones. For separate samples, the chloride binding capacity of concrete in atmosphere zone was the lowest, and would decrease with corrosion time in marine environment. The washing effect by tidal action would lead to the loss of Ca(OH)2, abrasion of surface, and decrease of compressive strength of concrete.

Rashad A.M., Mokhtar M.M., El-Nashar M.H., Abu-Elwafa Mohamed R.

Li H., Zhang Z., Deng Y., Xu F., Hu J., Zhu D., Yu Q., Shi C.

Rashad A.M.

Silica fume (SF) is a by-product of ferrosilicon alloys or the silicon metal industry. Due to its high fineness and amorphous silica, it is widely used in Portland cement (PC) systems as a cementitious material to enhance the durability and mechanical properties. In recent developments, numerous studies have been implemented to obtain superior properties of various types of geopolymer by incorporating SF. On the whole, SF can be recycled into geopolymers in three various forms: as an additive to the precursor or as a part of a precursor, as a part of an activator or as a foaming agent. Recycling SF into various geopolymer types may have a positive effect or an adverse effect. This mainly depends on precursor/SF fineness, activator concentration and type, activator/binder ratio, testing age, curing condition, SF amount and Si/Al ratio. The target of this document is to review, summarize and analyse the past studies focused on the effect of SF, in its three various forms, on the properties of geopolymers.

Rashad A.M.

Due to the prospective properties of silica fume (SF), it is frequently used in Portland cement (PC) systems as a supplementary cementitious ingredient to improve the mechanical and durability properties. In recent developments, numerous studies have been implemented to obtain superior properties of various types of geopolymer by incorporating SF. In spite of SF can be incorporated into geopolymers in various forms, most of the past studies employed it as a part of precursor/an additive. However, recycling SF as a cementitious material (as a part of precursor) into various geopolymer types may have a positive effect or an adverse effect. This mainly depends on precursor/SF fineness, activator concentration and type, activator/binder ratio, testing age, curing condition, SF amount and Si/Al ratio. The target of this part is to review, summarize and analyse the past studies focused on the effect of SF, as an additive or a part of precursor, on workability, setting time, density, mechanical strength and different durability aspects of various types of geopolymer.

Rashad A.M.

In spite of silica fume (SF) can be incorporated into different geopolymer types as a part of precursor, as a part of activator or as a foaming agent, most of the earlier studies employed SF as a part of cementitious material (as a part of precursor or an additive) (~ 74.1%), whilst employing it as a part of activator came in the second place (14.81%). Finally, employing SF as a foaming agent came in the last place (11.11%). In this part, the percentage of studies about the effect of SF as a part of precursor on each property of geopolymers was established and compared. The effect of SF in its three forms (part of precursor, part of activator and foaming agent) on the various geopolymer types was summarized.