Improvising the Self-Healing Capabilities of Concrete Using Different Pozzolanic Materials and Crystalline Admixtures

A Ravitheja ,T Chandra Sekhara Reddy ,C Sashidhar

(1.SVR Engineering College,Ayyalur,Nandyal,Kurnool,Andhra Pradesh,India;2.Civil Engineering,G Pulla Reddy Engineering College,Kurnool,AP,India; 3.Jawaharlal Nehru Technological University,Anantapur,India)

Abstract: To analyse the self-healing capacities in terms of mechanical performance of the pozzolanic materials,such as,fly ash,metakaolin and silica fume and crystalline admixtures.Pre-cracked concrete cubes with about 0.05 mm width were exposed to four different environmental conditions at different exposure times in order to determine the effect of temperature and water availability on the self-healing potential.After the exposure,the control and tested concrete cubes were evaluated for regained strength,void reduction,corrosion inhibition,damp proofing,relative impermeability and durability.The samples with SF10CA have better cementitious filling and low percentage of voids and water absorption.

Key words: crystalline admixtures;pozzolanic materials;self-healing

1 Introduction

Concrete is the most extensively used material in the construction industry.It is a heterogenous mixture of cement,water,fine aggregates and coarse aggregates.They are inexpensive and readily available throughout the globe and also supports modern infrastructure.Over 3.5 billion tonnes of Portland cement clinkers are produced globally and the global cement industry causes emission of 6%-7% of anthropogenic carbon dioxide.Many modifications have been done in the past few years to produce a better version of concrete with higher compressive strength,workability,durability,crack resistance and permeability resistance for reduction of carbon footprint.Moreover,the development of blended cement concrete with pozzolanic mineral admixtures seems to be one of the practical solutions for such desired mechanical properties.Also,such high quality,low cost blended cement concrete is suitable for infrastructural development in developing countries like India.

Addition of admixture cement concrete improves the microstructures of the concrete and decreases the concentration of calcium hydroxide (CaOH) through pozzolanic reaction.Further modifications in the microstructure of cement composites improves the mechanical performance and extends the services life of the concrete.However,the key to achieve a strong and durable concrete depends on the careful proportioning,mixing and compacting of the ingredients.According to Folagbade,blended cement concrete by virtue of their delayed strength development at early ages are essential for mass concreting and concrete work in hot climate than Portland cement alone.Admixture with fine pozzolana particles easily dissipates in the cement concrete and further generates huge nucleation sites for the precipitations of the hydrations products.Presence of amorphous silica in the pozzolanic materials initiates cement hydration reactions with CaOH produced by cement during concrete processing.In recent years,such high performance and inexpensive concrete blends are commonly used in the developed countries like United States for the construction of large projects in metropolitan areas.

Cement blends with pozzolanic mineral admixture are usually resistant to freeze-thaw cycles,alkaliaggregate reactions,reinforcement corrosions,

etc

.However,these properties were found to be improved when ultrafine mineral admixtures such as silica fume and metakaolin were incorporated into the mixture.

Silica fume is a secondary product produced during the silicon metal and ferrosilicon alloy production.It contains more than 80%-85% SiOin amorphous form.Such high proportion of SiOacts as filler and fits between cement grains.Such high pozzolanic property of silica fume makes it more suitable for use in the cement and concrete industries.Metakaolin,a thermally activated alumino-silicate material is produced by calcinations of pure or refined kaolinitic clay at 650-850 ℃.Also,as a processed amorphous silica material,it contains about 50%-55% of SiOand 40%-45% of AlOand is also highly reactive.Fine particle of metakaolin results in closer packing of the materials.More nucleation sites accelerate the hydration reactions,increase pore refinement and enhance concrete performance.Unlike others,metakaolin is a primary product which can be produced in a controlled process to achieve the desired properties.

Fly ash is a major secondary product obtained upon the combustion of pulverized coal in thermal power plants.It is well accepted pozzolanic material that can be used either as a component of blended portland cements or as a mineral admixture in concrete.Its availability,low cost and admixture properties makes it a primary pozzolana for blended cements.It is characterized by low water demand and reduced water/cement ratio due to its spherical shape and electronic dispersion.Unlike at the early age,pozzolanic reactivity improves its resistance in concrete mixture at later ages .

The use of mineral admixture like fly ash,silica fume and metakaolin adds strength and durability to the concrete.The presence of both pozzolanic and chemical admixtures in high performance blended cement results in improved rate of hydration and strength when compared with the traditional cement concrete.

The effect of mineral admixtures on the properties of concrete mixtures have been studied previously but the present study comparatively analyses the effect of fly ash,silica fume and metakaolin on the regained strength,compressive strength,microstructure of selfhealed cracks,chloride ion penetration,corrosion inhibition,void percentage and damp proofing of pre-cracked cement cubes exposed at different environmental conditions and durations.

2 Experimental

2.1 Material and their properties

This section presents the details of the experimental programme of high strength concrete (M70),mixing procedure,casting,curing,self-healing and testing of HSC specimens.The present study involved five different mixtures for the self-healing analysis.In this proposed work,the control mixture materials that were used are cement,fine aggregates,coarse aggregates,water,steel fibres and super plasticizer.Here,ZUARI brand cement OPC (Ordinary Portland Cement) with 53 grade was utilized,for satisfying the desires of IS:12269-1987 having the specific gravity of 3.12.The study performed various tests for the identification of physical properties of the cement.A normal consistency of 32% and compressive strength of 53 N/mmwas obtained.Local obtainable sand was possessed from river Tungabhadra,utilized as fine aggregate.The following tests were conducted on natural fine aggregate according to IS:383-1987.The sand was confirmed to Zone-II according to BIS.The fine aggregate underwent specific gravity and sieve analysis tests.Sieve analysis was performed for determining the size of particle distribution of fine aggregates as per IS:2386 (PART I)-1963.The determined values of specific gravity and fitness module for the fine aggregate were 2.57 and 3.22 respectively.In the present work,crushed aggregate from local quarry was utilized as natural coarse aggregate.In the analysis,12.5 mm aggregate was utilized and verified as per specification of IS:2386-1963 (I,II,III).The calculated values of specific gravity and maximum normal size for coarse aggregate were 2.70 and 12.5 mm respectively.Locally available potable water confirming to IS 456-2000 was found to be satisfactory for making the concrete.For this investigation,the water drawn from drinking water source was used for making concrete and curing.Water is being added to concrete mainly for hydration and workability.

Crystalline admixture is the second type of mixture,comprising proprietary mix of active chemicals.The high hypdrophyllic nature makes it a suitable carrier of sand and it is capable to retort with cement particles,water and also with cement hydration products (CaOH) of soluble phase forming C-H-S (calcium silicate hydrates) and rest precipitates of pore blockage.Crystalline admixture comprises of a mixture of micro silica,sand and cement.Reddy

et al

recognized that a concrete comprising of 10%silica fume had an effective crack healing capability and had strength regained capacity with 100% in water immersion and in condition of water or dry cycles.Hence,the mixture of crystalline admixture and 10%silica fumes has been selected as the third type of mixture analysed in the study.

Ding &Lievidenced that higher chemical shrinkage was identified when configuration with replacement of metakaolin up to 15%,and further reduced the configuration with a replacement more than 15%.In this regard,the fourth type of mixture considered for this study was crystalline admixture with 15% metakaolin.Finally,crystalline admixtures with 20% fly ash was taken for the analysis because an analysis done by Lucasindicated that 20% fly ash shows the best compromise between healing efficiency and compressive strength.The self-healing performance of the concrete cubes was evaluated by performing compressive testing machine (CTM).The measurements of surface crack width were pre-cracked by splitting.

2.2 Experimental methodology

The methodology utilized in this study evaluates the effects of self-healing in pre-cracked cement cubes which comprises of five steps:

2.2.1 Creation of damage:pre-cracking process

Pre-cracking process was carried out to test the self-healing performance of the concrete for 28 days.(Fig.1).

Fig.1 Schematic representation of the test set-up for crack fabrication

Initially,cured concrete cubes were removed from water after specific curing time.Excess moisture from the concrete surface was wiped and the dimension of the cube surface was measured.CTM surface was cleaned and the cube was centrally placed on the base plate of CTM.A rebar was introduced at the centre of the base plate to cause strain on the concrete cubes.The movable portion of CTM was adjusted such that it touches the top surface of the concrete cube.

2.2.2.Exposure simulation

Pre-cracked concrete cubes with maximum width of about 0.05 mm was exposed to four different environmental conditions (Fig.2) namely,Water Immersion (WI),Wet-Dry Cycles (WD),Water Contact(WC) and Air Exposure (AE) to determine the effect of temperature and water availability on the self-healing capability of the tested cement cubes.

Fig.2 Four exposure conditions:(a) water immersion,(b) wet-dry cycles,(c) water contact and (d) air exposure

The cracked specimens were cured for four different curing conditions for 7 to 42 days.For the present research,four environmental exposure conditions were deliberated in determining the effect of water availability over the self-healing feature of the verified samples,and associating referral concrete with crystalline admixture and metakaolin are shown below.

Water Immersion (WI):Continuous immersion in tap water at laboratory conditions with water addition to compensate any loss due to evaporation;Wet-Dry Cycles (WD):Immersion in tap water and air exposure for 3 days each;Water Contact (WC):Water layer of 2 cm was maintained on one surface,with addition of extra water for maintaining the level;Air Exposure(AE):Specimen storage at laboratory conditions without any external effects on condition of air.

2.2.3 Regained strength analysis

Since the self-healing properties are projected to increase,a corresponding increase in the value of stiffness and cracking loads are expected from the stage of initial loading to reloading.Self-healing efficiency(

R

) was employed to calculate the improvement in selfhealing strength using Eq.(1) given below:

2.2.4 Microstructure analysis

The microstructure of the healed crack formed on the surface of control and cement cubes with CA was investigated using Zeiss Crossbeam 540 scanning electron microscope (SEM).Factography coupled with energy dispersive X-ray analysis (EDX) were used to analyze fracture surfaces as well as to detect quantitatively the fundamental composition and recognize the phase formation.

2.2.5 Determination of pH and Caconcentration

The Caconcentration and pH at concrete or steel interface is the significant parameters influencing the process of corrosion and rate of corrosion in reinforcement of steel.Control Concrete (CC),Concrete with Crystalline admixture (CCA),CCA with 10% Silica fume,CCA with 15% metakaolin and CCA with 20% fly ash were used wherein pH value and Caconcentration in these mixtures were examined as a premise to understand the cracking and spalling of concrete and the healing properties of different mixes.

3 Results

3.1 Recovery of compressive strength analysis

The influence of various exposure periods to WI,WD,WC and AE use of through-crack compressive stress and the capability of various replacement in generating self-healing ability of material were analyzed wherein the fallouts of the selected specimens’compressive strength are represented in Fig.3,

When the regained strength of pre-cracked RC,CA,FA20CA,MK15CA and SF10CA was compared with each other under different environmental conditions,the following was observed:

When compared to the reference concrete,the regained strength of pre-cracked concrete with crystalline admixture was superior at all ages (7,14,21,28 and 42 days) for different concrete cubes as given in Fig.3.This is because,catalytic reaction between calcium ions,by-products of hydrated and unhydrated cement particles form C-S-H and calcite helps in self-healing.Hence,CA helps to bind cracks with maximum width of about 0.05 mm,imparting considerable mechanical strength recovery.

When compared to concrete cubes exposed to WD,WC and AE,samples exposed to WI was found to be significant in self-healing.This is similar to our previous findings which showed the importance of water in aiding healing materials because of the fact that healing materials has better proliferation when samples are exposed to WI curing condition regardless of the state of mineral precursor used for healing cement cubes under water.

When compared to concrete with CA,fly ash,metakaolin and silica fume,recovery of strength by silica fume was significant under varying environmental exposure,followed by metakaolin,fly ash and crystalline admixture.

Crack healing efficiency over time was found to be increased from 28 days to 42 days.Therefore,cement cubes with CA healed under WI resulted over 91% healing efficiency in 28 days and over 102% in 42 days when compared to CA healed under WD 87% and 101%,CA healed under WC 79% and 84% in 28 days and 42 days respectively.Moreover,the results were higher than the control.

Fig.3 Regain compressive strength of RC,CA,FA20CA,MK15CA and SF10CA due to structural cracks healing under different exposures compared with reference concrete:RC=Reference concrete;CA=Crystalline admixture;FA20CA=Crystalline admixture with 20%Fly ash;MK15CA=Crystalline admixture with 15% metakaolin;SF10CA=Crystalline admixture with 10% Silica fume

When compared to reference concrete,concrete cubes with CA were able to absorb moisture from the atmosphere.Hence,the results were not negligible for healing in AE with more than 70% self-healing efficiency at 28 days.

3.2 SEM with EDS results

Figs.4,5,6,7,8 show the formation of crystals and blocking of voids.Higher crystalline formation was observed with SF,followed by MK,FA and CA,while in the control cement cubes,the cracks/voids were left uncovered with no crystalline formation,and similar results were observed by Azarsa

et al

.These images are adequate indicators of crystalline admixtures performance in closing voids and cracks.The length of the crystalline were up to 10 µm and the shape varied due to the difference in composition and development.The microstructural investigation of CA shows C-S-H gel and CaCO.The SEM micrographs shown in Fig.4 indicates a reduction in calcium hydroxide crystals Ca(OH)with a subsequent increase in the formation of amorphous C-S-H gels and CaCOfor crystalline admixture concrete,resulting in stronger and durable concrete cubes.

Fig.4 SEM and EDS images of control concrete

Fig.5 SEM and EDS images of crystalline admixture

Fig.6 SEM and EDS images of crystalline admixture with 10%silica fume

Fig.7 SEM and EDS images of crystalline admixture with 15%metakaolin

Fig.8 SEM and EDS images of crystalline admixture with 20%fly ash

3.3 FTIR results

An FTIR quantity was achieved in attaining further particulars regarding the components of reaction products after self-healing.FTIR transmission spectra of the control concrete,crystalline admixtures,crystalline admixture with 15% metakaolin,crystalline admixture with 10% silica fume and crystalline admixture with 20% fly ash are presented in Fig.9.

Fig.9 FTIR transmission spectra of self healing concrete:RC=Reference concrete;CA=Crystalline admixture;FA20CA=Crystalline admixture with 20% Fly ash;MK15CA=Crystalline admixture with 15% metakaolin;SF10CA=Crystalline admixture with 10% Silica fume

Fourier transform infrared spectroscopy (FTIR)spectra analysis was conducted for structural analysis through confirmation of reaction occurred by detecting characteristic absorption band of different functional groups present on the healed surface.The FTIR graph is presented in Fig.5,where similar infrared bands were observed regardless of different sample types.Characteristic H-O-H bond stretching was noted around 3 620 cmfollowed by shallow wide transmittances,which indicated the presence of Portlandite Ca(OH).Following that,sharp bands around 1 424-1 430 cmand 870 cmconfirmed the presence of carbonate phases (CO) in all samples.The indication of ettringite presence was confirmed by the sulfate (SO)stretching vibrations around 900 and 1 418 cm.Similar findings were reported by researchers.The deep banding around 980 cmconfirmed the Si-O bonding for possible C-S-H presence.Researchers have further suggested that bending at 830 cmcould be an indication of CA incorporation in the C-S-H,as is evident in this case,although there was lots of noise effect in the signal for low range web numbers.While FT-IR results identified basic self-healing materials,the influence of CA in the healing compound formation was possible to distinguish.FTIR observations indicate the apparent complexity of the self-healing products formation due to CA addition with cement.Different proportions and CA addition influence will be further explained through the self-healing materials surface.Samples with only water immersion resulted mostly in Ca-rich products in the self-healing surface,such as calcite and C-S-H.These can be as a result of the following self-healing reactions:

3.4 Chemical analysis

3.4.1 pH value test results

The pH values of 5 different specimens before healing and after healing are measured and tabulated in Table 2.

The pH values of RC,CA,FA20CA,MK15CA and SF10CA were measured to understand the cracking and self-healing of concrete and the healing properties of different mixes.The pH of all tested samples was high before healing process.After healing,though the pH decreases slightly,it was not significant.When compared to RC,CA,SF10CA,MK15CA,pH of FA20CA was low before and after healing process.FA20CA showed the least pH under WI.

3.4.2 Calcium (Ca) concentration

The calcium (Ca) concentration was also calculated for all the selected five different specimens before and after healing and was presented in Table 3.

The concentration of CaCOwas measured to understand the healing properties of different mixes.The resultant nucleation sites promoted cement hydration,which lead to production of C-S-H gel,and CaCOfurther enhanced the strength of cement material.Crystalline admixture with 10% silica fume had higher calcium concentration compared to other selected specimens.Crystalline admixture with 15% metakaolin showed greater calcium (Ca)concentration.

The concentration of CaCOwas measured in order to understand the healing properties of different mixes.The resultant nucleation sites promoted cement hydration,which led to the production of C-S-H gel,and further enhanced the cement material strength.Crystalline admixture with 10% silica fume had higher calcium concentration than all other selected specimens.Crystalline admixture with 15% metakaolin showed greater calcium (Ca) concentration.

3.5 Durability of self-healing concrete

The percentage of shrinkage in RC,CA,FA20CA,MK15CA and SF10CA recorded at 7th,14th,21st and 28th day are shown in Fig.10.It is evident that the percentage of shrinkage of SF10CA remained constantly lower when compared to other cement cubes with crystalline admixtures due to high rate ofevaporation.However,shrinkage percentage of all CA remained lower when compared to the control.Though the percentage of shrinkage of FA20CA and MK15CA remained the same at 7th day,shrinkage in FA20CA gradually increased when compared to MK15CA.CaCOformation has been considered as a prominent internal crack healing product,which mainly depends upon the conditions of exposure and cementitious material types.

Table 3 Calcium (Ca) concentration before and after healing

Fig.10 Percentage of shrinkage

3.6 Rapid chloride permeability test (RCPT)of self-healing concrete

RCPT was conducted on RC,CA,FA20CA,MK15CA and SF10CA to test relative impermeability.The total charge generated is determined to assess the chloride resistance of concrete and is shown in Fig.11 and Table 5.When 1 000 to 2 000 coulombs represent low chloride permeability,100 to 1 000 represent very low chloride permeability,the samples were tested for a period of 6 hours at all tested ages from 28 days.It was observed that coulomb charge for SF10CA was found to be lower followed by FA20CA,MK15CA,CA and control indicating more resistance to chloride penetration.

Fig.11 Chloride ion charge

3.7 Percentage of water absorption and voids of self-healing concrete

The percentage of voids and water absorption of RC,CA,FA20CA,MK15CA and SF10CA at the age of 28 days was recorded and represented in Fig.12 and Fig.13.From the figures,it is evident that decrease in the percentage of voids (cracks) decreases the percentage of water absorption.Hence,sample SF10CA which have better healing and cementitious filling has shown low percentage of voids and hence,low water absorption.Though all samples showed noteworthy reduction in the percentage of voids and water absorption from control (2.827) and (1.635),the reduction in percentage of voids and water absorption recorded by MK15CA (1.132) and (0.695) and SF10CA(0.954) and (0.496) was significant.

Fig.12 Water absorption

Fig.13 Percentage of voids

4 Discussion

The present work attempts to examine the complications of self-healing concrete with reference to the ordinary strength fiber reinforced concrete.The self-healing effect was excellent for concrete with crystalline admixtures in WI and WD due to the demand for water.The self-healing efficiency of cracks dropped for AE and concrete without crystalline admixture.When all the different mixtures were compared,it was revealed that SF1CA could selfhealing better than other materials which makes it the best pozzolanic material for mixing with cement as shown in Fig.14.

This formation of CSH and other hydration products densified the matrix and reduces the permeability of the chloride or reduces the carbonation resulted in reduced corrosion.Addition of admixtures,reduces the alkalinity of concrete cubes,which helps to fill the space and hardens the concrete reducing its porosity or permeability.Hence,admixtures reduce pH of cement concrete to some extend that is necessary for hydration reaction.Carbonation by addition of SF,results in reduction of CaOH,which reduces the alkalinity of the cement cubes.From the results,it is clear that SF show greater carbonation when compared to other specimens.Similar findings were reported in Poli,however,it should be noted that cement cubes with SF maintains pH at an adequately high level to protect steel.

CA showed high percentage of drying shrinkage when compared to others (CA and cement &CA and other mixtures) because,with increase in replacement ratio and ageing,the percentage of drying shrinkage reduced considerably.Addition of fly ash (FA) helps in reducing drying shrinkage percentage.Similar results were observed by Sounthararajan &Sivakumar.This is due to the fact that FA has significant effect on the porosity of concrete which greatly affects the percentage of drying shrinkage.Also,studies by Yang

et al

and Sounthararajan and Sivakumar,proved that increase in the percentage of FA content,significantly reduced the percentage of drying shrinkage.However,study by Akkaya

et al

,showed that addition of FA increased the percentage of drying shrinkage due to the decreased elastic module of the concrete and difference in void structure connectivity leading to moisture escape.

Metakaolin (MK) along with crystalline admixture(CA) reduces the size of pores,void connectivity and pre-stressing influence which results in shrinkage reduction.MK is a highly reactive pozzolana and its reaction mechanism can be divided into physical and chemical aspects.In its physical effect,the ultrafine particles fill the voids in cement,which makes the microstructure of matrix denser.Chemically,MK reacts with the cement hydrates in a faster approach due a loose microstructure after heat activated at a temperature of 800 ℃ (the chemically bonded water in kaolin is driven out at a higher temperature,and water molecules enter MK more easily when met with water again).During the chemical reaction,the precipitated calcium hydroxide (Ca(OH)) is transformed into secondary C-S-H (C=CaO;S=SiO2;and H=HO) gel,resulting in refinement of the pore structure(transformation of coarser pores into finer pores).Owing to the net reduction in Ca(OH)content,the volume of continuous capillary pores is proportionally decreased;the higher the Ca(OH)content in the hydrated matrix,the higher the volume of continuous pores.

The diffusion of chlorides through the concrete is mainly due to the microstructure of the concrete and the fixing ability of ions.Anhydrous compound tricalcium aluminate,spontaneously reacts with chlorides in cement.Therefore,admixture with high content of tricalcium aluminate is recommended to ensure the integrity of the steel of reinforced concrete exposed to chloride rich environment.

Fig.14 Self-healing photos of concrete with pozzolanic materials and crystalline admixture under water immersion (WI)

Low chloride penetration in SF10CA indicates better healing and cementitious reaction in cracks when compared to other samples.7% SF provided a significant chloride penetration resistance and further increase in the percentage of SF (upto 12%) reduced the diffusion coefficient.However,study by Lizarazo-Marriaga and Yépezreported that when increment in the percentage of SF upto 15% showed negligible penetration.Good chloride penetration resistance by SF is believed to be due to its high tortuosity and the refinement of the pore structure.

Studies by Dhinakaran

et al

and Li

et al

reported that chloride penetration resistance by MK was due to its filler effect,followed by acceleration of cement hydration and finally,by means of pozzolanic reaction with CaOH formed during the cement hydration.Also,15% MK showed better performance which was similar to our findings.Reduction in chloride penetration in concrete cubes with FA was also reported by Cabrera

et al

and Boğa &Topçu.Apart from increasing the durability of concrete,addition of FA,helps in reducing the pores by production of additional cementitious compounds,change pore structure and further in reducing the water content requirement.Moreover,the study also reported that ageing increases formation of crystalline products and discontinuous pore structure which aids chloride penetration resistance.High pozzolanic effect of SF resulted in compactness and densification of microstructures in concrete cubes.According to Zhang

et al

,addition of SF,reduces the content of CH,to form calcium silicate hydrates (C-S-H gel) and addition of raw SF with cement concrete refined the pore structure by its chemical reaction and reduced the pore size by its physical filling effect.Similar properties were observed in MK which lead to the formation of secondary C-S-H gel structures,increasing concrete strength and reducing voids along with CaCOformation.This increases durability of the concrete cubes.X-ray diffraction on MK formation of ettringite reported that CaCOin cement reacts with aluminates in MK to produce hemicarboaluminate and monocarboaluminate crystalline structures.Such structures refine the pore structure and reduces void in concrete cubes,hence,reduces porosity.

Reduction in void and water absorption by addition of FA to concrete cubes was also reported by Saha.However,slow pozzolanic reaction of FA in formation of secondary C-S-H gel and filling micro void was attributed because of its large particle size and small surface area.Hence,SF is superior among others in reducing the percentage of voids and water absorption.

5 Conclusions

High pozzolanic,greater carbonation,low chloride penetration and high tortuosity of cement cubes with SF10CA,results in better healing,compactness and densification of microstructures and maintenance of adequate pH.This leads to better binding of cracks with considerable strength recovery,corrosion inhibition of steel and good chloride penetration resistance.Hence,samples with SF10CA have better cementitious filling and low percentage of voids and water absorption followed by samples with MK15CA and FA20CA.

6 Limitations and future recommendation

Though the study has considered both primary products such as metakaolin and secondary products such as silica fumes and fly ash as cement admixtures,the results confirm that silica fumes were superior admixture when compared to metakaolin in terms of better self-healing properties.Hence,further studies on cost efficiency of these admixtures are warranted.Due to time constraints,the study was limited to analyze the mechanical performance of these pozzolanic materials.The second limitation of the study is the amount of admixture.It is important to vary the amount of pozzolanic materials to standardize the correct ratio as the amount used in this study was not standardized.The study further recommends the combinations of different pozzolanic materials as each material has its own pros and cons.