Behavior of non-reinforced and reinforced green mortar with fibers

2.1 Materials

Ordinary Portland Cement (OPC) type (CEM I) of strength class 42.5N was used in this study. It is obtained from Sulaymaniyah cement factory, Bazian district, Kurdistan, Iraq. Clear waste glass powder and Steel slag powder (prepared by ball mill machine) were supplied from glass recycling plant andiron production factory, Mosul, Iraq respectively. The specific gravity and fineness of these materials were measured according to ASTM C188 [65] and ASTM C204 [66]. Chemical composition of both Clear waste glass powder(WGP) and steel slag (SG) powder were examined using a XRF-1800 Sequential X-ray fluorescence spectrometer. According to ASTM C618, (SiO₂ + Al₂O₃ + Fe₂O₃) the minimum requirement for a standard pozzolana is 70% which is comparable with the results obtained for the clear waste glass and steel slag samples. As per ASTM standard mentioned above, the maximum limit of SO₃, Loss on Ignition (LoI) and Moisture content is 4%, 10% and 3% respectively. As list in Table 1, the SO₃ contents of clear waste glass powder and steel slag powder was less than the acceptable limit, Loss of ignition (LOI) and moisture content have been neglected. Minor compounds such as ZrO₂, TiO₂, CuO, Cr₂O₃, NiO, MnO, As₂O₃ are also found in clear waste glass and steel slag samples under consideration, the amount of individual component was not more than 0.5%. Densified Micro-silica (SF)was procured from MSASA-Construction Solutions for Africa, Pomona AH, South Africa.

The chemical composition and physical properties of OPC, WGP, SG and SF are given in Table 1. The sand used for preparing of non-reinforced green mixes was prepared according to 20-30 sand requirements ASTM C778 [67]. Its specific gravity was measured according to ASTM C 128 [68] and was 2.590. Whereas, the sand used for preparing reinforced green mixes was prepared according to graded sand requirements ASTM C778 [67]. It was used to obtain a homogeneous mixture containing fibers, the specific gravity was 2.577. Superplasticizer obtained to enhance the workability of mixes was procured from Specialties construction chemicals factory, Jahra, Kuwait. Its commercial name is KUT PLAST PCE 600. The properties of superplasticizer are shown in Table 2. Tap water was utilized in all mixes.

Three different types of fibers used in this study were sisal fibers, human hair fibers and stainless steel nails in mono and hybrid fibers system. Sisal fibers (SIF) were brought in bundles form with length 1 meter approximately. They were separated and cut into (18 ± 2) mm before using them in the mixes. They were supplied from local markets, Mosul, Iraq. Human hair fibers (HHF) were obtained from local hair salons, Mosul, Iraq. They were washed, separated, combed and cut them into (18±2) mm before adding them to the mixes. Stainless steel nails (SNF) were procured from local markets, Mosul, Iraq (Figure 1). SIF and HHF were used in 0.5, 0.75 and 1% of volume fraction. (SNF) were used in 1, 1.5 and 2% of volume fraction. The properties of three different types of fibers are presented in Table 3.

Figure 1

Fibers utilized in this study

2.2 Mix proportions

In this research, total forty one [41] mixes were prepared; Ten [10] of them were prepared to measure pozzolanic activity for each of waste glass powder, steel slag and silica fume. Binder/sand ratio was 1:2.75, water/binder ratio (W/B) was 0.59, and the mix proportions of these mixes are shown in Table 4.

Moreover, nineteen [19] mixes were prepared to produce non-reinforced green mortars, binder/sand ratio was 1:2.75, water + superplasticizer/binder ratio (W+SP/B) was 0.39, the mix proportions of these mixes are listed in Table 5.

Another twelve [12] mixes were prepared by substituting 8%, 12% and 10% of cement by WGP, SG and SF respectively and using three different types of fibers (sisal fibers, human hair fibers and stainless steel nails) with different percentages of volume fraction to produce reinforced green mortars, binder/sand ratio was 1:2.75, maximum superplasticizer dosage (2%) by weight of cement was also used in these mixes as listed in Table 6.

3.1 Experimental method

Ten [10] mixes were prepared to measure the pozolanic activity of solid waste materials (waste glass powder, steel slag and silica fume) by following steps: a) Cement and solid waste material were mixed for 1 to 2 minutes. b) Then, the sand was added and mixed with the mixture for 1 to 2 minutes. c) Tap water was added to the mixture and mixed for 2 to 3 minutes. Non-reinforced green mixes were prepared by the same steps mentioned above, except that the superplasticizer was mixed with tap water before adding into the mixture. Reinforced green mixes were prepared by the same steps mentioned above. Then, the fibers were added gradually in to the mixture.

At least three [3] specimens were cast for all mixes. These specimens were prepared at room temperature (25±2^∘C). After 24 hour of molding and humidity not less than 75%, the specimens were demolded, immersed in tap water and treated up to 7 and 28 days.

Flow test was conducted for each mix according to ASTM C1437 [69]. Dry density test was conducted for 70.7×70.7×70.7mm specimens at 28 day according to ASTM C642 [70]. Ultrasonic pulse velocity (UPV) was performed through 70.7×70.7×70.7 mm specimens at 28 day as per to ASTM C642 [70] after thirty minutes of taking them out of water. The compressive and flextural strength tests were applied on 50×50×50 mm cubes and 40×40×160 mm prisms at different ages (7 and 28 days) by using ASTM C109 [71] and ASTM C348 [72] respectively.

Motorized Cement flow table was used for measuring flowability of mixes. Laboratory oven was used to determine the mass of oven-dried sample and the mass of surface dry sample after boiling for 5 hours. Specific gravity apparatus was used to calculate apparent mass of the sample in water. Ultrasonic tester was utilized for measuring the propagation time of ultrasound pulses with a precision of 0.1 μs through 70.7×70.7×70.7 mm specimen. Hydraulic compression testing machine (300 kN capacity) was utilized to measure compressive strength and flexural strength for 50×50×50mmand 40×40×160mmsamples, respectively, at age 7 and 28 days.

3.2 AHP and TOPSIS methodology

3.3 Technique for Order Performance by Similarity to Ideal Solution (TOPSIS)

TOPSIS is a simple and useful approach which is used to deal with the complex system related to making a best choice among several alternatives [77]. It was developed by Ching-Lai Hwang and Yoon in 1981. The concept of this technique is based on the selecting the ideal alternative which has the shortest distance from the positive ideal solution and the farthest distance from the negative ideal solution [62]. In this research, TOPSIS was used to select and rank the best of reinforced green mortar based on its properties. In addition this technique was also used to determine and rank the best and worst non-reinforced green mortar based on its impact on the environment. The ranking and determining of reinforced and non-reinforced green mortars was achieved using the following steps:

4.0.1 Pozzolanic activity index (PAI)

The average of three values of compressive strength of mortar prepared for measuring the pozzolanic activity of waste glass powder, steel slag or silica fume are shown in (Figure 2). The ratio between compressive strength of mortar containing supplementary cementitious material (waste glass powder, steel slag or silica fume) and compressive strength of control mortar at the same age is called activity index which assesses the pozzolanic activity of the supplementary cementitious materials as displayed in (Figure 2). The results indicate that the compressive strength of mortar containing waste glass powder or steel slag decreases with increases cement. The reduction of the strength can be attributed to the reduction of the amount of cement and the pozzolanic activity variation of these materials and cement.Moreover, the presence of these materials in cement past lead to delay of C₃S and C₃A hydration at early age and the activity of the compounds (SiO₂ + Al₂O₃ + Fe₂O₃) of waste glass powder or steel slag is less than the activity of the same compounds of cement [23, 78].

Figure 2

Activity index at 7 and 28 days

Although, The use of waste glass powder and steel slag led to slightly decrease in the strength, these materials are considered in this study due to its pozzolanic activity. As per ASTMC 618 [79], the minimum requirement of strength activity index for a standard pozzolana is 75% at age 7 and 28 days. Therefore, Waste glass powder and steel slag are considered as pozzolanic materials due to the strength activity index of waste glass powder and steel slag, at replacement level 20%, was 87 and 86% at age 7 days and 80 and 79% at age 28 days respectively.

Also, the strength activity index of silica fume was examined according to ASTM C1240 [80]. The results indicate that the strength activity index of silica fume, at replacement level 10%, is 112 and 104% at age 7 and 28 days respectively. As per ASTM C standard mentioned above, the minimum requirement of accelerated pozzolanic activity index of silica fume is 85% at age 7 days. Therefore, this material is considered as pozzolanic material in this research. Moreover, the results indicate that the compressive strength of mortar containing replacement ratio of cement by 10% of silica fume show the highest compressive strength in comparison with other mortars. Indeed, the high fineness, high content of amorphous silicon dioxide of silica fume and sufficient content of calcium hydroxide acquired by hydration of cement play a significant role on improvement production of calcium silicate hydrate (C-SH) supplying additional compressive strength [19].

4.0.2 Workability

Table 9 exhibits the flowability of non-reinforced green mixes. This table indicates that the flowability of the mix decreases with increases the replacement ratio of cement by silica fume or/and steel slag. The high specific surface of silica fume leads to more quantity demand of water for hydration and for flowability [21, 33, 81]. In contrast, waste glass powder content in mix does slightly increase of flow mix by increasing replacement ratio of cement. It might be the effect of glass material which is cleaner in nature. This result is supported by recently studies which conducted by other researchers [33, 82].

On the other side, the results in Table.10 indicate that the folwability of green mix reduces due to the addition of the sisal fibers. This can be attributed to the amount of cellulose which forms (43-56)% by weight of sisal fibers [83]. The large quantity of hydrophilic hydroxyl groups which containing cellulose make sisal fibers are water-absorbent [84]. The same trend at adding human hair fibers to the mix.

Indeed, the chemical composition of cortex and cuticle, which consisted of human hair fiber, rich of keratin peptide bonds as well as to hydrophilic side chains (phenolic, carboxyl, amino, hydroxyl, guanidine, etc.) which contribute to absorption of water [85]. Therefore, addition human hair fibers to the mix led to reduce its flowability. But, the inclusion of stainless steel nails in the mix increases the flowability of mortar as shown in Table 10. This is may be attributed to low porosity and softness of the surface of this type of fibers as well as shape of roller tapered of stainless steel nails.

In hybridization case, it is observed that the flowability of reinforced green mixes with hybrid fibers M10 and M11 was decreased obviously. Therefore, water-binder ratio was increased to 0.58 for obtaining flowability 80% and 60% for M10 and M11 respectively as shown in Table 10. The reduction of flowability of M11 was higher than M10. This can be attributed to the amount of sisal fibers and stainless steel nails which was used in the both mixes. The increment of sisal fiber volume fractions and reduction of stainless steel nails volume fraction in M11 led to decrease its flowability compared with M10.

4.0.3 Compressive strength

Table 9 lists the results of the compressive strength of non-reinforced green mortar. The results indicated that the compressive strength of mortars containing replacement ratio of cement by waste glass powder and steel slag was decreased in comparison with control mortar (U1) at 7 and 28 days. The decreasing rate was by 21.345, 0.778 and 9.895% at age 28 days for U2, U3 and U4, respectively. And by 22.937, 18.137 and 34.020% at age 28 days for U5, U6 and U7, respectively, in comparison with control mortar. So, the replacement 15% of cement by waste glass powder or steel slag boosts the best performance in comparison with 10 and 20% replacement ratio of cement.

Moreover, the results of mortar using of the mixture of waste glass powder and steel slag as partial replacement of cement indicated that the compressive strength was reduced in comparison with control mortar at 7 and 28 days. The reduction was by 20.914, 15.878, 19.803, 20.884, 19.245 and 24.794% at age 28 days for U11, U12, U13, U14, U15 and U16, respectively. And, the reduction of compressive strength was by 27.294, 25.397 and 20.487% at age of 28 days for the mixes U17, U18 and U19, respectively, compared to control mortar.

The reduction of mortar strength containing waste glass powder or /and steel slag can be attributed to the decreasing of the amount of cement in the mix and the contribution of the hydration or the pozzolanic reactivity of waste glass powder or steel slag did not compensate for the reduction of the cement content [86]. Moreover, the presence of slag in cement mortar leads to slightly delay the hydration of C₃S at early age where slag acts as retarder to the hydration of compound C₃A [87].

Although, the results show that the presence of waste glass powder and steel slag led to decrease the strength, the reduction of the strength of mortar containing waste glass powder was lower than mortar containing slag. This is attributed to the high content of amorphous of silicon dioxide (72.71%) and the sufficient content of Na₂O in waste glass powder. Indeed, the presence of Na₂O in acceptable level led to act as a catalysts in forming calcium silicate hydrate in early age [78, 86].

While, the results of the mortar containing replacement ratio of cement by silica fume indicate that the compressive strength increases with increase silica fume content in the mortar compared with control mortar. The increments were by 6.211, 7.594 and 21.162% at age 28 days for U8, U9 and U10, respectively.

The increases in the compressive strength can be attributed to the decreased volume of large pores in the cement mortar and the spaces between fine aggregate and cement past due to its high fineness [63, 78]. Moreover, silica fume have significant role on the reducing of Ca(OH)₂ resulted from cement hydration by reacting with it to form C₃S₂H₃ [63, 78]. Thus, the presence of silica fume was enhanced the strength of mortar in this study.

On the other side, the drop in compressive strength of mortar containing silica fume, waste glass powder and steel slag blended cement can be attributed to the reasons mentioned above regarding to the presence of waste glass powder and steel slag. Although, the silica fume contributes to increase the strength of mortar the agglomeration of silica fume, which cannot be broken down by normal mixing, lead to decrease the strength. The core of agglomeration does not take part in hydration. Thus, it cause the weakness in binder paste [29].

Table 10 shows the results of reinforced green mortar with mono and hybrid fibers. This Table shows that the compressive strength of M1, M2 and M3 was increased by 0.420%, 7.412% and 0.630%, respectively, at age 28 days compared with control mortar M0. The higher increase was observed at M2 then the compressive strength of M3 was demonstrated the reductions by 4.081 and 6.314% at 7days and 28 days respectively. The increase in compressive strength may be attributed to identical SIF percent and bond strength between the surface of sisal fibers and composites of mortar which led to diminish of porosity of hardened mortar [59].

While, reinforced mix by 0.5, 0.75 and 1% of human hair volume fractions led to increase the compressive strength of mortar by 3.321, 9.416 and 2.089% at 28 days respectively. This enhancement in compressive strength come back to the proper amount of HHF which did not lead to cause balling and lumping of HHF during the mixing process as well as high modulus, high tensile strength of HHF and its ability to reduce the micro-fractures or cracks of hardened mortar [54]. Also, it can be seen that the inclusion 1% of HHF in the mix led to decrease the compressive strength by 1.532 and 2.089% at age 7 and 28 days respectively in comparison with M5 as listed in Table 10. This reduction can be attributed to the agglomeration of HHF during blending with composites of mortar which has resulted in non-homogeneity mix as noted by [50].

Moreover, the results in Table 14, indicates that the compressive strength of M7, M8 and M9 increased by 3.290%, 5.372% and % 15.380, respectively at age 28 days in comparison with control mortar (M0). The increasing of compressive strength can be ascribed to the good mechanical bond strength between the stainless steel nails and mortar.

For hybrid fiber reinforced mortar, the compressive strength of M10 and M11 has shown increment by 1.744 and 0.035%, respectively, at age of 28 days, compared with control mortar.

4.0.4 Ultrasonic pulse velocity (UPV)

Table 9 illustrates the results of ultrasonic pulse velocity test (UPV) of non-reinforced green mortar. The results indicate that the UPV of mortar containing waste glass powder and steel slag was decreased compared to control mortar. The decreasing recorded rate ranged from 2.632 to 10.506% due to partial replacement of cement by WGP. Also, there were remarkable decreases of UPV due to the partial replacement of cement by SG. Such decreases ranged from 8.626 to 21.986% by such replacement. In contrast, the mortar containing replacement ratio of cement by the silica fume exhibited slight increases of UPV. The increasing rate ranged from 0.774 to and 4.246% by partial replacement of cement with SF. The grain size and high quantity of hydration products (C-S-H and CH) of silica fume in comparison with WGP and SG led to reduction in porosity and void ratio of hardened mortar [86]. Thus, UPV of mortar containing silica fume higher than UPV of mortar containing waste glass powder or/and steel slag.

The similar trend for mortar containing WGP, SG and SF blended cement. UPV results revealed mild to moderate decreases by the inclusions of different percentages of such cementitious materials.

However, the highest reduction of UPV has been obtained due to replacement of cement by to WGP and SG which has less efficiency compared with silica fume resulting in porosity and void ratio increases in the hardened mortar which cause decreasing in UPV [87].

The results in Table 10 indicate that the UPV of sisal fiber reinforced mortar, Human hair fiber reinforced mortar and stainless steel nail reinforced mortar showed higher values of UPV than that of control mortar. The increases in such values ranged from 0.603 to 9.492% for mixes (M1-M9). Moreover, the results of mortar containing hybrid fibers showed that the UVP of M10 and M11 increased by 1.454 and 0.274%, respectively, compared with control mortar. This can be attributed to good mechanical bond between the fibers and cementitious matrix and the ability of fibers to arrest cracks at the micro and macro levels which leads to densify of the microstructure and decrease the cracks and porosity in hardened mortar.

4.0.5 Flexural strength

The results of flexural strength of non-reinforced green mortar are given in Table 9. The results indicate that the flexural strengths of mortar containing waste glass powder or/and steel slag were decreased in comparison with control mortar (100%OPC). This can be attributed to the same reasons mentioned in compressive strength. However, a slight increase in flexural strength of mortar prepared by 90% OPC+10% SF has been recorded.

While, the results indicate that the flexural strength of mortar containing mono or hybrid fibers was higher than control mortar as listed in Table 10. The highest increases were 15.131, 10.577 and 69.261%at age 28days for individual fibers form 0.75% SIF, 0.75% HHF and 2% SNF. The developing of the flexural strength can be attributed to the good mechanical bond between the fibers and cementitious matrix. The presence of fibers, on the other hand, had a beneficial effect on the post-crack behavior, promote the flexural strength and ductility and hence toughness of the mortar [43]. The increasing of flexural strength was mainly observed in the reinforced mortar containing higher volume fraction of stainless steel nails due to the high elastic modulus of stainless steel nails compare to other fibers.

In hybridization case, It is observed that the flexural strength of M10 and M11 was higher than of control mortar. The increases were by 19.788 and 16.704% respectively, at age 28 days. Moreover, the increment of the flexural strength of M9 was higher than that of M10 and M11. The increments were by 41.299 and 45.034% at age 28days, respectively. The use of mono stainless steel fibers shows a significant increment of flexural strength for mortar. While, the use of this type of the fiber with sisal fibers and human hair fibers in hybrid form led to decrease the flexural strength in comparison with mortar containing stainless steel nails in mono form. This can be attributed to clearly decrease the flowability of reinforced mortar with hybrid fibers. Besides of that, some of sisal fibers and human hair fibers were agglomerated leading to cause non-homogeneous mix.

4.0.6 Dry density

Table 9 depicts the results of oven dry density of non-reinforced green mortars. The obtained results indicate that the dry density of control mortar (100% OPC) was higher than mortar containing waste glass powder or/and steel slag. The decreasing of the density can be ascribed to the greater variation between pozzolanic reactivity of cement and supplementary cementitious materials (waste glass powder and steel slag) which led to increase the voids ratio and the porosity in hardened mortar. In contrast, the density of mortar containing silica fume. The results indicates that the density of mortar U8, U9 and U10 was higher than of control mortar (100%OPC). The increasing was by 0.176, 0.750 and 4.545% respectively. This is because of high amount of amorphous silicon dioxide made by silica fume to reduce Ca(OH)₂ provided by cement hydration to form calcium silicate hydrate gel [39, 54]. Moreover, the high fineness of silica fume made it acts as filler material and because of which fits the spaces between cement past matrix and the aggregate cement paste interfacial zone leading to improve the density of hardened mortar [20]. Also, it is observed that the dry density of M1, M2 and M3was higher than Control mortar(M0). The increasing was by 3.095, 3.476 and 3.285% respectively as shown in Table 10. The same trend for M4, M5 and M6, there was little increasing by 3.476, 4.333 and 1.761% respectively. The reason can be attributed to good mechanical bond between cementitious matrix and fibers. Moreover, the use of sisal fibers and human hair fibers can contribute to fill the micro space in cementitious matrix leading to improve the density. Moreover, the inclusion of 1, 1.5 and 2% volumetric fraction of stainless steel nails led to increase the oven dry density. The increasing was by 6.380, 8.476 and 10.619%for M7 ,M8 and M9 in comparison with control mortar (M0). This is because of high specific gravity of stainless steel nails and ability of this type of fibers to improve inter-facial bond characteristics between the matrix and fibers.

For hybridization mixes, the results Indicate that the dry density of M10 and M11was increased by 7.619 and 3.523, respectively, in comparison with control mortar (M0).This enhancements are attributed to appropriate ratio uses of sisal fiber, human fiber and stainless steel nails volume fraction which led to improve the microstructure of matrix [48, 54].

4.1 Estimation of green mortar cost

The estimated cost of reinforced green mortar was evaluated on the basis of the different materials which were used to prepare green mortar as listed in Table 11-12. The estimated cost of each material was depended on the existing market cost.

4.2 Selection of the best green mortar

The integrated AHP and TOPSIS method was also used to rank and select the best reinforced green mortar. In this stage, there were twelve [12] alternatives and four [4] criteria of reinforced green mortars. The alternatives were represented the reinforced green mortars. The criteria were represented the properties of the reinforced green mortar which were Compressive strength, Flexural strength, UPV and Cost. Based on AHP method, the weight for each criterion was calculated. The matrices and results, which were obtained through applying of AHP method to evaluate the criterion weight,were illustrated in Table 13-14. The checking of pair-wise matrix (F) was achieved according to the step 4 which was previously mentioned in the general steps of AHP method. The results were listed in Table 15. The consistency index (CI) obtained was 0.020 and the random consistency obtained from Table 8 was 0.9. Thus, the pair-wise comparison matrix was considered in this study due to the consistency ratio was 0.022. Then, TOPSIS method was applied to rank the reinforced green mortars. The raw data used in the TOPSIS technique, were listed in Table 16. The matrices and the results obtained from this technique were show in Table 17-18. Table 19 showed that the second mix of the reinforced green mortar is the best as it got the rank 1 and the ninth mix is the worst mix as it got the rank 11.