The Physical Properties Study of The Hybrid One-Part Alkali-Activated Mortar

One-part alkali-activated materials (AAMs) are an alternative material to respond to the shortcoming of the conventional two-part systems. One-part AAMs are more practical and safer to handle from transporting to the casting stage on site. It can be applied in the form of paste, mortar, and concrete, providing more options than an ordinary cement binder. The most common aluminosilicate precursors sources for the one-part AAMs are the combination or single raw material of fly ash, ground granulated blast furnace slag and metakaolin. However, it was found that the one-part AAMs experienced high porosity levels primarily due to their inconsistent pore structures that affect their long-term performance. One-part AAMs mortar is one of the cementitious products used as concrete repair materials that may be affected by these weaknesses. Nevertheless, the combination of aluminosilicate precursor by-products with the ordinary Portland cement or hybrid AAMs help to develop a robust performance mainly used as a patching product for concrete repair materials. This hybrid one-part AAMs mortar can be composed with other admixtures with a suitable mix design to ensure its stability and useable in the form of a fresh and hardened state. Unlike the


Introduction
Yang et al. [1] reported that one-part slag paste activated by a 15% sodium carbonate alkali activator demonstrated higher pore diameter and pore volume than a 10% sodium carbonate alkali activator suggesting that excessive alkali activator could coarse the pore structures.The average pore diameter decreased from 24.29nm to 21.48nm with adequate compressive strength up to 41MPa at 28 days.A higher concentration of alkali activator encourages the product to be more dense and solid without decreasing any unreacted particles.Still, it has also affected the porosity level between 30 -40% for one-part AAMs composed of calcined commercial kaolin and calcined ceramic waste, as reported by Azevedo et al. [2].Gel pores and capillary pores are two significant concerns on the strength of cement paste where gel pores are unlikely to affect much strength properties but are reported influential on creep and shrinkage [3].However, not all finer pores are harmful.There are four ranges of pore sizes that influent the compressive strength of hardened AAMs, which are classified as harmless pores for sizes below 20nm, less harmful pores for 20 -50nm, harmful pores if 50 -200nm and more harmful pores if exceed 200nm [4].It was reported that two-part AAMs composed with a single metakaolin precursor used as concrete repair materials recorded 2.0MPa maximum bond strength, but 20% replacement with slag showed improved pull-off bonding strength as an indication of mixed aluminosilicate precursors exhibit greater strength than a single type of binder source.Both compositions have documented about 14% porosity level [5].
A rectangular micro structure on the surface can be formed by increasing the alkali activator in a dry mixture, as reported by [2].However, excessive alkali content in the mixture can migrate to the surface and react with CO 2 in the atmosphere, subsequently causing carbonation.The use of hybrid one-part AAMs concrete studied by [6] demonstrated that the inclusion of 30% OPC in the mixes has more compact microstructures and less unreacted fly ash particles compared to 0 -20% of OPC content but has a more porous structure than 40% and 60% of OPC content.The compressive strength for one-part AAMs concrete with 60% OPC was about 55.0MPa, while for 40% OPC and 30% OPC recorded about 52.0 MPa and 50.0MPa respectively at 28 days of age, activated by 3 to 5% of alkali activator.One-part AAMs composed of single precursors of metakaolin promote a highly porous structure, heterogeneous with unreacted particles that affect its mechanical strength and durability as recorded in SEM images [7].In contrast, Askarian et al. [8] reported that one-part AAMs composed of fly ash/slag have denser microstructure than fly ash only mixes to confirm that combination of aluminosilicate precursors contributes better mechanical strength, rich in Al but has a substantial low Ca/Si ratio where in contrast, hydrated OPC provide much higher Ca/Si ratio.This experiment further examines the microstructure of fly ash/slag precursors mixed with the OPC, also known as hybrid one-part AAMs using SEM and EDX, to support the compressive strength result and to study the micromorphological features of the mixes in the form of hydrated particles.Hybrid one-part alkali-activated mortar in the experiment activated by different water to cement ratios of 0.30, 0.35 and 0.40 to encounter previous findings which stated that alkali-activated materials exhibit higher porosity level and larger pose size than those reported in ordinary Portland cement (OPC) paste, hence by controlling water to cement ratio, could produce less porous polymeric microstructure [9], increasing the mechanical strength at a later stage and reduce porosity level, as a primary focus of the work in this report.

Material and method
Class f -Fly Ash (FA) and Ground Granulated Blast Furnace Slag (GGBFS) were used as precursors under ASTM C618 and ASTM C989, respectively.Ordinary Portland Cement (OPC) was added as the primary binder source and activated with alkali-activated powderpotassium carbonate (K2CO3 Purity ≥ 90%).The FA, GGBFS and OPC chemical compositions are shown in Table 1A, 1B and 1C.Natural sand was used as fine aggregates with a specific gravity of 2.67 and an average particle size of 90.23um (D50).In addition, a commercial ethylene glycol type of shrinkage reducing admixtures (SRA) and calcium oxide (CaO) was added as admixture and expansion agent, respectively, in the form of solid powder.At the same time, the sodium lignosulfonate powder-based superplasticizer (SP) was also used in the experiment based on a previous study on the potential admixtures for one-part alkali-activated materials (AAMs).Water is then added to activate the dry mixes and tested in the fresh and hardened state.The particle size distribution for all particles is measured by Laser-diffraction Analysis (LDA), as shown in Table 2.

a. Mix Proportions
The experimental study was conducted to understand the physical properties of one-part alkaliactivated mortar activated with different water binder ratios to improve the workability, mechanical strength, and durability.The microstructure of the mortar in this experiment was also analysed using the Scanning Electron Microscope (SEM) All the samples were marked as G1, G2 and G3 and consisted of FA, GGBFS and OPC as main precursors with different volume percentages.Sample G1 is a control sample chosen based on the author's previous study.The admixtures proportion for every sample was added into the mortar samples between 0.30 to 1.0 wt% of weight based on total aluminosilicate precursors (binder) weight.The water to binder ratio was set between 0.30, 0.35 and 0.40, and the binder to sand ratio was constant at 1 to 1 to produce the mortar and cured under controlled temperature as a reference from the past reports.The compositions of one-part alkali-activated mortars are further elucidated in Table 3 based on the author's previous study.

b. Sample preparations
An electric mixer, EX-EM2000 EXTRAMAN 2000W, was used to prepare all mixes.The FA, GGBFS, PCC, K2CO3, SRA, CaO, Sodium Lignosulfonate (SP) and fine aggregates were blended in the mixture for 2 minutes according to their sample of mix compositions.After that, water was added slowly to the mixtures and continued blending for another 3 minutes to ensure the mortar paste was uniform.Then, all the fresh mortars were immediately cast into a 40mm x 40mm x160mm mould for the compression strength test.All filled moulds were vibrated for 2 minutes using a shaking table.The mixtures were demoulded after 24 hours before being cured in controlled lab temperature of 20 +/-2 Celsius, with Relative Humidity (RH) of > 90% until the testing day on 7, 28 and 56 days of curing age.
For setting time test of fresh mortar, it follows the same procedure.Still, after 3 minutes of mixing with water, the samples are immediately cast into Vicat moulds before the penetrating process begins at a specific time interval.The preparation of fresh mortar for setting time and pull-off strength test was under a controlled temperature of 20 +/-2 Celsius and Relative Humidity (RH) > 90%.Then, the mixing steps are repeated to prepare samples for the Flow Table test of mortar but under lab ambient temperature between 29 -30 Celsius and Relative Humidity (RH) between 55 -60%.Then, fill and compact fresh mortar into a truncated conical mould at the flow table platen before jolting the samples.

c. Experimental procedures.
The one-part AAMs mortar was mixed following the dry mixing method in previous studies.
Compressive strength (CS) of hardened mortar was evaluated at 7-d, 28-d and 56-d curing age to study mechanical strength and properties.The compression test machine AUTOMAX5 was used at a loading rate of 2.4 +/-0.2kN/s.The mean value of three readings of each sample produced in triplicate for every test was recorded and taken as their final strength value.Test on the setting time of mortar was conducted by penetrating the fresh mortar in Vicat moulds, set with 120 minutes for its first interval.The height of the Vicat mould is 40+/-0.2mm,and the initial setting time was recorded when the 34+/-3mm was obtained, and the final setting time was recorded at 0.5mm penetration depth obtained as per MS EN 196-3: 2016 specification.For the flow table test, after the truncated conical mould is removed, then the flow table is jolted 15 times and measured using a calibrated calliper.The average of two spread dimensions was recorded to get the flow value according to BS EN 13395-1-2002 standard.The workability of the one-part AAMs mortar determines by observing how easy the fresh mortar deforms when stress is applied.Table 4 above showed that sample Mix G3 which is activated by water to a ratio of 0.30, has the shortest initial and final setting time, followed by sample Mix G2 and control samples Mix G1.CaO, GGBFS and rich calcium-based OPC decreased the setting time of one-part AAMs [10] significantly.Nevertheless, in this study, water content was the main factor differentiating between all samples mortar.Lower water to binder ratio can shorten the setting time due to heat generation from solid activators when reacted with water.Askarian et al. [6] found that paste only contained fly ash and slag did not set within 24 hours and recorded the shortest setting time by incorporating 60% OPC in the mixes.However, a quick setting could prevent proper casting at a site besides transporting issues from the batching plant.As for the flow table test, the higher water content in sample Mix G1 spread up to 153.7mm compared to the samples with a lesser water ratio content samples mix G2 and G3.It is worth noting that the finer the particles are, the lower the spreading flow is [4].All mixes contained similar particle sizes and were examined using Laser diffraction Analysis (LDA), as shown in Table 2.All mortar samples were spread firmly, and no segregation was found on the flow table.Workability of the mortar is beneficial when applied as a repair patching material to ensure the patched mortar remains firm, set and bonded well on a substrate.It can also be concluded that the addition of 70% OPC can accelerate the setting time of one-part AAMs within an acceptable initial and setting time range, better than other findings reported in past research.The optimum water to binder ratio of 0.3 exhibits the best performance for fresh one-part AAMs mortar setting time and workability.cementitious materials for proper workability and strength.This result confirmed that the lower the water/binder ratio, the higher the hardened mortar's compressive strength.Moreover, the lower binder to the sand ratio used in this study was set to 1, beneficial to acting as reinforcement in the matrix and providing high dimensional stability to the mortar, improving mechanical performance and adherence level [11].Apart from that, the compressive strength of one-part alkali AAMs product in this experiment keeps increasing after 28 days of age and confirms the geopolymerization process remains active.The water content difference affected the hydration products and strength development.Luukkonen et al. [12] In one-part AAMs, four steps occur after water is added to cementitious materials, beginning with ion exchange, hydrolysis, network breakdown and release of Si and Al, which differentiate the one-part technology from the conventional two-part AAMs.It is worth mentioning that as the geopolymerization cycle continues, the cracks and pores formed at the early stage were filled with the increasing amount of gels and justify compressive strength development over time as the result of a reduction in the accumulated volume of the pores, mainly from C-A-S-H gels phase fill the pore structure to reduce the pore diameter[1] [13].The compressive strength of one-part AAMs containing fly ash, OPC and slag as the main component reacted with alkali activator to produce gel formation of sodium aluminosilicate hydrate (N-A-S-H), calcium alumino-silicate hydrate (C-A-S-H) and stable 3D network of silico-aluminate structures that enhance polycondensation process that contribute to the higher compressive strength [14].

Mortar
The inclusion of lignosulfonate as a retarder in this study could improve the dissolution of slag, OPC and CaO powder, subsequently increasing compressive strength as reported by [14] superplasticizer (SP) dosage and reducing water amount caused high compressive strength of AAMs cementitious products.Differences in SP effect on one-part AAMs depend much on the stability behaviour of admixtures in a different type of solid activator.The use of a low dosage of potassium carbonate as a solid activator in this study has reacted well with sodium lignosulfonate type of SP, effectively reducing the water content up to 15% to improve compressive strength in good agreement with [15].The compressive strength development is correlated with the fine and large pore's diameter [16].With this regard, the compressive strength of the one-part AAMs mortar was also investigated by the pore structure in the latter part of this report.The inclusion of shrinkage-reducing admixture (SRA) and CaOexpansive agent contributed to the higher compressive strength for its role in mitigating shrinkage by reducing the surface tension of pore water and micropores.When water is added, the SRA helps decrease internal stress during evaporation, while CaO counteracts the shrinkage's effect by reducing the capillary stress.The porosity level, however, can be controlled by diminishing the capillary stress of the water generated by SRA during the mortar mixing process, although reported as a setback in affecting the elasto-mechanical properties of ethylene-glycol-based admixture [16].Quicklime-CaO was used as an expansive agent in mortar.Adding the CaO with SRA has increased the mortar volume instead of shrinking it like conventional cementations materials.
The expansion of mortar is lengthened with the inclusion of CaO during the hydration process and only starts to shrink when the wet curing is stopped.The combination of CaO and SRA reported gave a better performance concerning cracking resistance of the mortar, which is beneficial for better the mechanical properties of hybrid one-part AAMs [17].Higher water content could decrease the yield stress and plastic viscosity of fresh cementitious materials and affect their rheology behaviour and mechanical strength at the hardened stage.The water content can be adjusted and change the yield stress and plastic viscosity.Still, in real construction, the W/B are conventionally controlled to ensure homogeneity of the mortar or concrete, besides practical handling from mixing and transporting to pouring time.Cement particles begin to dissolve and hydrate when contacted with water.This reaction produced positive and negative charges on the cement surfaces and created electrostatic activities among cement particles, leading to flocculation of the particles.As a result, the portion of the water will be wrapped in the cement particles, and the free amount of water will be decreased, leading to a higher content of good solid volume fraction.The yield stress and plastic viscosity level subsequently rise with the increase of solid volume friction and improve the workability of the fresh one-part AAMs mortar [18].With a constant proportion of binder, percentage of alkali activator, and dosage of admixture for every mortar sample in this study, the lower water content of W/B ratio of 3.0 will be reduced the most, followed by W/B of 0.35 and 0.40.Higher yield stress and plastic viscosity ensure the fresh mortar is more stable and flows consistently, but too viscous could be an advantage if applied as sprayable mortar as it is not easy to be pumped out from the pipe.On the contrary, lower W/B with higher slag content also reported a setback in autogenous shrinkage and cracking [14] due to its porosity and pore size reported larger than the OPC [9], which is further discussed in the later section in this report.noting that pores sizes in the range of 3.5 -10nm are commonly described as small gel pores type, while 10 -100nm are better known as large gel pores [19], 50nm -10um as capillary pores that cause detrimental to the strength of hardened samples and voids if the pore size is more significant than 10um [13].Voids or air bubbles have less impact on the strength during the sample preparation process triggered by vibration or moulds defects [20].Small average pore diameter in this experiment as a sign of the complete reaction process of the products that can fill capillary pores with the addition of slag could decrease polymerization degree and improve pore size distribution of the mixes and strength development as reported by [8].

Sample
The increase in porosity percentage will decrease the mechanical strength performance of hardened one-part alkali-activated materials [2].On the other hand, mortar sample Mix G3 has an overall better pore structure distribution in terms of a low percentage of porosity of 16.655% only, higher density, smaller median pore diameter and low total pore area compared to mortar sample Mix G2.This much contributed to a high concentration of ordinary Portland cement able to decrease microstructure porosity with the formation of amorphous Ca-Al-Si gels [6] and discussed further in the microstructure analysis section of this report.In comparison to other one-part AAMs, Samarakoon et al. [3] reported that the porosity level for one-part fly ash/slag-based materials was 35.96% (activated by sodium silicate/sodium hydroxide solution), 39% porosity (activated by soda lime glass powder/ sodium hydroxide) and 29% activated by solid sodium silicate.For two-part AAMs, Kramar et al. [21] stated that the higher porosity level was recorded for metakaolin-based mortar (16.5%) followed by fly ash mortar (13.2%) and slag mortar (11.1%).It is interesting to note, as published in the report, that only metakaolin-based mortar has complied with class R4 standard and class R3 for fly ash-based AAMs, as per EN1504 specifications, with a larger range of average pore diameter between 20 -140nm detected in two-part AAMs mortar samples compared to the one-part alkali-activated mortar samples in this experiment to summarize that the hybrid one-part AAMs introduced in this report has not only improved the existing one-part AAMs performance but also comparable to the two-part AAMs system for concrete repair application.
Furthermore, the total pore area occupied under controlled lab temperature curing mortar at a water-cement ratio of 0.35 is 21.431 m 2 /g and 17.374m 2 /g for mortar samples with a watercement ratio of 0.30.The decrease in porosity is due to the enrichment of pore structures as an effect of the dense and compact hybrid one-part alkali-activated mortar where the group of aluminosilicate C-A-S-H gels characterized the geopolymer matrix Si-O-Al network that reflects porous fundamental structure in geopolymerization process to refined the pores [13].
The ongoing alkali activation at a later stage encourages more pore structure refinements, which is the main factor in the highest compressive strength recorded for samples Mix G2 and Mix G3 at 28 days in the previous experiment.Samarakoon et al. [3] reported that one-part AAMs activated by the dry activator of NaOH micro-pearls or solid NH have coarse pore fraction more than 20nm of the total porosity subsequently prone to the chemical attacks and potential of lower resistance against severe curing conditions than two-part AAMs counterpart but in contrast, findings from this report indicate that lower dosage of potassium carbonate react with optimum water-cement ratio of 3.0 in geopolymerization process is capable of refining the pore size of the mortar by filling the capillary pores subsequently increasing the degree of microstructure densification and in a good agreement with higher compressive strength recorded.The microstructure of hybrid one-part alkali-activated materials was studied using Scanning Electron Micrograph (SEM).The fractured mortar surfaces were taken from the compressive strength test sample at 28 days of age.It was produced with different percentages of mix composition consisting of fly ash which contains 25% of total precursors weight, 5% ground granulated blast furnace slag and 70% ordinary Portland cement, which donated to the densified microstructure of the mortar.All raw materials used in this study from aluminosilicate precursors, alkali activators and solid admixtures have good reactivity and are well dissolved when in contact with water.The hydrolysis of all these solid activators facilitates the network breakdown of solid precursors.Dissolved ions would undergo gelation and condensation, as reported by Lv et al. [22].
A higher volume of OPC is beneficial to wrap the water in the cement particles and reduce the amount of free water in the fresh mortar mixes, subsequently increasing adequate solid volume friction for better compactness and leading to higher mechanical strength [18].Three exothermic reactions after the addition of water in one-part AAMs are dissolution of raw materials (NaOH and hydration of CaO), bond breaking (attack of OH -on Si-O and Al-O bonds) and release of Ca, Si and Al and formation of gels via polymerization as reported by [12].Unreacted particles decrease in quantity with a longer curing time and a higher dosage of alkali activator in the system.A higher percentage of OPC content in the mix contributes to a more compact and less porous structure and less unreacted fly ash particles but also comprises both unreacted and partially reacted OPC particles, as agreed by [6].Few spots were captured for the image, and only images with overall textures, i.e., pores, and cracks, reacted.Unreacted particles are selected in this report to understand the microstructures of the hydrated particles.
The morphology of the two mortar samples is similar from the perspective of porosity, aggregate-mortar interface, and some unreacted particles.Fig. 1 and Fig. 2 showed that both SEM images for samples G2 and G3 are well hydrated, compact, and homogenous with the larger formation of new hydration products, mainly calcium sodium aluminosilicate hydrated C-(N)-A-S-H type of gels on its surfaces and the usage of dry activator type of potassium carbonate contribute to lesser unreacted calcium.Hence, the Silicon phases show the reacted phase's homogenous nature [3].Both images also depict the reacted, unreacted textures, including micropores and microcracks marks, but also exhibit a glass-like surface representing the geopolymeric gel.
Fly ash particles composed of microspheres, amorphous alumina and/or silica-rich materials can be dissolved in alkalinity [23].The spherical particles will be embedded in the form material and contribute to a better mechanical strength.Spherical structured are spotted in the image, commonly known as the unreacted fly ash component in agreement with Azevedo et al. [2] on the fact that fly ash particles remain even after contact with alkaline materials in all curing periods, probably caused by low alkaline reactivity.It was also helpful to understand that some unreacted particles are inherited from the parent material of hydration products, as suggested by [9].SEM images zoomed with 20um specifically at spherically shaped areas revealed that sample G2 has a less unreacted spherical structure than sample G3, which consists of more spherical spots, as shown in the Fig. 3 and Fig. 4.However, it can also observe in this image that the pores of sample G2 are more prominent, which supports the pore structure distribution result; therefore, the unreacted particles could act as micro fillers in the mixes and improve its compactness in general.A compact structure shows good adhesion and explains the increase in mechanical strength of the mortar (Fig. 5 and Fig. 6).The compaction of microstructures improved with a more extended curing period, confirming the increment of strength over time for both mortar [24] samples as recorded in the compressive strength test at 7 and 28 days of this age report.Both images have shown microcracks spots.Although a line of microcracks is more visible in the mortar sample G3 image may indicate the loss of water [25], temperature cracks due to the heat generated from the reaction between sodium oxide of alkali activator and water [8] and uneven shrinkage forces between derivatized gel and the particles, all take place during curing period [19].The cracks' formation could degrade the mechanical performance of the mortar over time.Though, Almalkawi et al. [9] reported other factors on why microcracks could appear or get visible area due to the drying process of the specimen for scanning electron microscopy (SEM).The clear microcracks image proves that the mortar sample G3 has a higher average pore diameter than G2, in line with the MIP test result for pore structure distribution.It was reported that 8% solid activator (by weight %) used to activate FA/GGBFS one-part AAMs only achieved about 30MPa at 28 days of curing age where more unreacted particles observed in SEM image if alkali activator used less than 8% subsequently recorded lower compressive strength [10].In contrast, lesser unreacted particles are observed on both SEM images for samples G2 and G3 in this experiment yet achieved significant compressive strength value proved that hybrid one-part AAMs activated by the low dosage of alkali activator have substantial potential to improve the current technology of onepart AAMs.
Alkali activated materials concept is much contributed by the dissolution of aluminosilicate precursors with the formation of geopolymeric gels consisting of low atomic order favourable for hardened materials cementing properties [2].The preparation of samples was conducted under controlled temperature and not exposed to high temperatures that could trigger dissolution.On the other hand, the geopolymerization begins with the calcium reacting with potassium carbonate to create C-S-H gels, consequently elevating the pH of the alkaline mix, and reducing water content.Under an alkaline environment, the dissolution of aluminosilicate precursors was initiated, subsequently ameliorating polycondensation and polymerization reaction for the hardening process.The precipitated compounds and geopolymeric gels of N-A-S-H and C-A-S-H contributed strength and remained to develop higher over time as the geopolymerization continued.On the contrary, at a higher temperature level of 65 Celsius, the dissolution of aluminosilicate precursors quickens to form geopolymeric compounds at an early age for higher early strength.Still, it may also cause incomplete dissolution of aluminosilicate compounds given that geopolymeric slurries could cover the undissolved precursor, limiting further dissolution besides water evaporation and excessive shrinkage problem create more cracks and pores and finally decrease the strength of the mortar [14].
Samarakoon et al. [3] reported that at the early age of curing, the hydration product for one-part AAMs is mainly composed of C-A-S-H type gels.However, the reaction products are moreover C-S-H dominant due to higher reactivity, and easier discharge of calcium ions can be found as early as 1 day of curing age.At the same time, the other portion of silicon and aluminium remains unreacted on the surface of the reacted phase.After 28 days, calcium content will be reduced.Still, silicon involvement in hydration products is increased because higher portions  The difference in the surfaces of the hybrid one-part alkali-activated mortar activated by different water to cement ratios was further investigated by the chemical element composition at a specific area using the EDX.The resulting SEM images at 28 days of curing with the corresponding EDX maps at 28 days of curing are shown in Fig. 7 -Fig.8 and Fig. 9 -Fig.10.
During the curing period, microstructures of all mortar samples become dense by reducing micro-pores, reflecting compressive strength development with time due to high compacted and low porosity levels [26].The formation and spatial distribution for both mortar samples consistently depict a well-blended elemental distribution for the formation of homogenous and dense microstructure [3].The reaction process in AAMs requires a few steps starting with the dissolution of Ca, Si and Al from aluminosilicate precursors, re-orientation process, reinteraction and condensation to develop the strength [20].Additionally, the chemical compositions of Ai/Al and/or Na/Si atomic ratios and K/Al molar ratio are beneficial to determining the mechanical properties of the AAMs, which is in connection with its products dissolution rate [23][27].It was explained in a past report on forming C-A-S-H gels that were regarded as aluminium substituted C-S-H phase in AAMs technology.Aluminium (Al) in C-A-S-H functioned in bridging tetrahedral sites.Still, the different extent was restricted by chemical limitations due to a defect of the tobermorite structure [22].The overall constituent of geopolymerization products for mortar samples G2 and G3 have consisted of newly formed hybrid geopolymeric products N-A-S-H gels co-exist with C-A-S-H gels.New hydration products of C-(N)-A-S-H type gel were confirmed using EDX point analysis on dominant elemental phases in the reacted cement binder, mainly silicon, calcium, aluminium, and sodium.Askarian et al. [6] reported that CaO to SiO2 (Ca/Si) decreases with decreasing OPC content in geopolymer mixes.Mixing with higher Ca/Si ratio is beneficial to form C-S-H gels which can improved the early strength of mortar.Ca/Si ratio for OPC has reported between 1.2 to 2.3 while the result from the EDX result showed that Ca/Si ratio of 0.96 for mortar sample G2 and ratio of 2.0 for mortar sample G3.Luukkonen et al. [28] reported that Ca/Si increases when LS introduced in the mortar with Ca 2+ reaction from lignosulfonate could facilitate the dissolution of slag to increase the amount of calcium and likely to increase the compressive strength of mortar.It is worth noting that 30% OPC total weight reduction in the mixes and were replaced with FA and slag yet still achieve a comparable Ca/Si ratio with sole OPC precursor.

Conclusion
It was reported that one-part AAMs experienced coarser pore fractions above 20nm, affecting their durability and mechanical strength compared to the two-part counterpart.A larger pore diameter will cause higher porosity and be prone to chemical attacks, especially when the location is exposed to adverse climate and temperature.This report established the improvement of one-part alkali-activated mortar composed of hybrid precursors between fly ash, slag and ordinary Portland cement and activated by the low dosage of alkali activator with controlled admixtures percentage level and smaller pore diameters which overcome the shortfall of current one-part technology.Other than that, this experiment also concludes few more explanations as follows: 4.1 The hardening mechanism and microstructures of hybrid one-part alkali-activated mortar changed significantly when the mortar was composed of different water to cement ratios, producing different mechanical strength at early and later stages, and affecting the pore structure distribution.For example, at 20 Celsius, controlled lab temperature and water to cement ratio of 0.30 demonstrated the highest compressive strength of 54.0MPa at 28 days and 63.0MPa at 56 days.

4.2
The ongoing alkali activation development in one-part alkali-activated mortar encourages continuous pore structure refinements, which is essential to control total porosity level and determine the mechanical strength of AAMs later.A significant lower porosity value below 20% was recorded for both mortar samples G2 and G3, respectively, which is beneficial to controlling the shrinkage level.

4.3
The SEM images at 28 days of curing age for mortar samples G2 and G3 show identical structures and similar final products.The only difference brought by different water to cement ratios was the amount of reacted geopolymer gels, unreacted precursors, size of micropores and microcracks.Both samples have homogenous reacted geopolymer gels, but more unreacted fly ash particles were observed in mortar sample G2.In addition, micropores were detected more for mortar sample G2, and average pore diameters were higher for mortar sample G2.

3. 4 Fig. 1 SEMFig. 3 SEMFig. 5 SEM
Fig.1 SEM Image: overview sample G2 Fig.2 SEM Image: overview sample G3 of fly ash could promote zeolite formation at the later curing stage.When the composition of the binder is SiO 2 -rich, the incorporation of Na is also favoured, subsequently confirming the co-existence between C-A-S-H and N-A-S-H with a potential cross-linked structure of C-(N)-A-S-H type gels at subsequent curing.The C-(N)-A-S-H type gels reported can resist leaching in aggressive environment and more stable under chemical attacks, beneficial for one-part AAMs long-term efficacy.

4. 4
Textures of particles can be observed via SEM images which support the mechanical strength results of the hardened mortar.Dense, compact, and homogenous microstructure of hybrid one-part alkali-activated mortar proved higher compressive strength at 28 days of curing age and satisfied class R4 EN1504 requirements for structural concrete repair materials.4.5A low dosage of alkali activator assists the geopolymerization process of hybrid aluminosilicate precursors consisting of fly ash, ground granulated blast furnace slag and ordinary Portland cement.Unlike the conventional one-part AAMs, dissolution of precursors is not completed under low alkaline reactivity, leading to a more significant number of unreacted particles.Declaration

Table 5 .
Mortar sample Mix G3 has recorded higher compressive strength for all curing periods beginning at 7 days of curing age and continues to develop later.
the minimum compressive strength requirement for class R3 -structural concrete repair products as per EN1504 standards.Water to binder ratio (W/B) significantly influences

Table 6 : Pore structure distribution result using MIP test.
Pore structure distribution of mortar samples Mix G2 and Mix G3 were analyzed with Mercury Intrusion Porosimetry (MIP), and the results are shown in

Table 6 .
The mortar specimens were collected from the crushed cube samples after the compressive strength test on 28 days of curing age.The median pore diameter is mainly distributed in the range size of 5.90nm and 6.15nm.The average pore diameter for both mortar samples have no significant difference with sample Mix G2, which has recorded 18.20nm and 19.52nm for sample Mix G3.It is worth