Effect of glass and polypropylene fibers in cementitious composites containing waste stone powder

Abstract

In this study, stone powder as a waste material was used to fabricate cementitious composite samples. Neat (non-modified) cementitious samples were composed of gravel, cement, sand, water, and waste stone powder. Flexural and compressive strength tests showed that flexural and compressive strength could be improved by increasing waste stone powder weight percentage. In addition, the experimental results illustrated that samples containing waste stone powder present more flexural and compressive strength in comparison with those fabricated without waste stone powder at constant cement weight percentage. In the next step, polypropylene and glass fibers were used in specimens containing waste stone powder. Consequently, flexural strength of fiber-reinforced composites was modeled by modifying “Equal Cross-Section Theory.” The results show that fibers increase flexural strength of specimens; meanwhile, waste stone powder does not have a significant effect on compressive strength. In another step, it was tried to make cementitious composite samples containing perlite as a light aggregate. Cementitious composites containing waste stone powder and perlite presented more flexural and compressive strength compared to samples without waste stone powder.

Keywords

Cementitious composite waste stone powder polypropylene fibers glass fibers perlite

Introduction

Today, the primary material and fundamental product for building construction in many countries is Portland cement. Concrete is one of the cement products used in many parts of building. The problem is the weight of the concrete. Therefore, lightweight aggregates (LWAs) can be used to solve this problem. Nowadays, using LWA in concrete includes several advantages such as reduction of dead load, production of lighter and smaller per-cast elements, reductions in size of columns and beam dimensions, higher thermal insulation, and better fire resistance [1]. Consequently, lightweight concrete made with natural and/or artificial LWA can be applied in a wide range of unit weights and strengths suitable for various applications including internal and external walls, inner leaves of roof decks and floors [2,3]. LWA concrete includes low density of 300–1200 kg/m³ for block production and medium density of 1000–2000 kg/m³ for structural concrete [2]. In this way, perlite is a common LWA. Perlite is a hydrated volcanic stone that increases in volume by heat [4]. High volume and low density besides insulation property of perlite has been led to using this material in building industry such as brick walls, plaster walls, panels, and floors. Using perlite in concrete reduces strength. Therefore, more cement should be used to fabricate the concrete for achieving expected strength [5].

On the other hand, Portland cement factories release a large amount of carbon dioxide to atmosphere – up to 13,500 tons per year, which is 7% of greenhouse gas produced annually [6]. Therefore, many researchers have recently focused to produce concrete by waste materials. A study by Tuan et al. used waste construction materials and waste glass powder in concrete. The concrete showed a reduction in water absorption and an increase in break point [7]. In another study, Posi et al. [8] conducted a feasibility study to making lightweight concrete by using waste block aggregates.

In addition, using fibers in concrete is common to improve flexural and tensile strength. Initial bonding between fibers and concrete can be assigned by physical adhesion and also static friction generated by surface finish of fibers. Chemical bonding between fibers and matrix is not strong in comparison with friction resistance. Fundamentally, increasing fiber length causes an increase in the friction resistance between fibers and matrix. This is because the specific surface of fibers will be increased in this case. Researches on fiber-reinforced concrete manifest that fibers control crack propagation during the initial loading of the structure [9,10].

Polypropylene (PP) and glass fibers are generally used to produce fiber-reinforced concrete. PP fibers can be produced as monofilament and/or as collated fibrillated fiber bundles. Their properties are related to the crystalline ratio and orientation [11]. PP reinforced concrete (at relatively low volume fractions <0.3%) are used for secondary temperature shrinkage reinforcement, overlays and pavement, slabs, flooring systems, shotcrete tunnel lining, canals, and reservoirs [12,13].

Glass fibers that are used in concrete, especially in lightweight concrete, improve tensile and flexural strength because of their high modulus. In addition, glass fibers can control shrinkage and resistance in alkaline environment [14]. Sivakumar et al. [15] studied on the plastic shrinkage cracking in high-strength hybrid fiber (such as polyester, PP, and glass) reinforced concrete. Results showed that hybrid fibers were most effective in reducing shrinkage cracks compared to steel fibers.

The main goal of this study is therefore to investigate the effects of waste stone powder (WSP) on compressive and flexural strength of cementitious composite structures. PP and glass fibers have been used to reinforce concrete samples filled with WSP. In addition, the performance of fibers within reinforced cementitious composites under flexural loading of cementitious composite has been modeled by using “Equal Cross-Section Theory.”

Materials and methods

An ordinary Portland cement (Type 1) was used in this study. The cement conforms to ASTM C150 [16] with a specific area of 3000 (g/cm²) and a specific gravity of 3.15 (g/cm³). The chemical composition of the cement is shown in Table 2. Natural river sand was chosen as fine aggregate. The course aggregate was derived by crushing limestone with diameter of 5–15 mm. PP fibers (12 mm length, 90 µm diameter, and 30% elongation) and glass fibers (40 mm length and 0.097 mm diameter) were used to reinforce cementitious samples. Table 1 shows physical and mechanical properties of fibers used in this study. WSP was used as a filler to fabricate different samples. After a stone is cut out by a stone-cutting machine, stone powders are mixed with the water of the machine and WSP is made. WSP is generally buried in the landfills beside the towns. Since the base material of WSP is lime, it makes the soil very alkaline that it is too wrecking for the soil and plants. Table 3 illustrates the chemical composition of WSP used in this study.

Table 1.

Physical and mechanical properties of fibers used in this study.

Fiber	Length (mm)	Diameter (µm)	Density (g/cm³) (ASTM D1577)	Module of elasticity (GPa) (ASTM C1557)	Tensile strength (MPa) (ASTM C1557)
PP	12	90	0.91	3.7	684
Glass (E type)	40	0.097	2.58	80	3445

PP: polypropylene.

Table 2.

Chemical composition of Portland cement used in this study.

SiO₂ (%)	Al₂O₃ (%)	Fe₂O₃ (%)	CaO (%)	MgO (%)	SO₃ (%)	Na₂O (%)	K₂O (%)	Loss (%)	In sol (%)	Density (kg/m³)
21.86	5.90	3.20	63.50	1.80	1.70	0.20	0.70	1.24	0.50	3150

Table 3.

Chemical composition of waste stone powder used in this study.

SiO₂ (%)	Al₂O₃ (%)	K₂O (%)	Na₂O (%)	CaO (%)	FeO (%)	Fe₂O₃ (%)	MgO (%)	TiO₂ (%)	P₂O₅ (%)	MnO (%)	Density (kg/m³)
72.04	14.42	4.12	3.69	1.82	1.68	1.22	0.71	0.30	0.12	0.05	2500

In addition, some samples were fabricated with perlite as a light aggregate to reduce the final density of the composite sample. Figure 1 shows the schematic of the experimental program.

Figure 1.

The schematic of the experimental program.

The standard size of the specimens used for flexural test was selected as 16 cm × 4 cm × 4 cm according to ASTM C348-86 [17]. After the flexural test, broken specimen parts were used for compressive test according to ASTM C349 [18]. In this study, an attempt has been made to use minimum cement for making specimens. Mix proportion shown in Table 4 was chosen as the basic mixture design.

Table 4.

Mix proportion of specimens without waste stone powder (weight percentage).

Mixture no.	Cement (%)	Water (%)	Sand (%)	Coarse aggregate (%)	Density (g/cm³)
C	10	9	53.44	27.56	2.13

Consequently, WSP with different weight percentages was added to make specimens according to Table 5. The gradation curve for WSP is shown in Figure 2.

Figure 2.

Gradation curve for waste stone powder.

Table 5.

Mix proportion of specimens containing waste stone powder (weight percentage).

Mixture no.	Cement (%)	Water (%)	Sand (%)	Coarse aggregate (%)	Waste stone powder (%)	Density (g/cm³)
CS1	10	10	48.33	26.67	5	2.17
CS2	10	11.66	38.33	30.01	10	2.24
CS3	10	11.83	40	23.17	15	2.28
CS4	10	12.66	38	19.34	20	2.31

Consequently, specimens were put in water (21 ± 2℃) for 27 days. In the next step, flexural and compressive tests were carried out on all specimens shown in Tables 5 and 6. Therefore, 20% WSP (CS4 sample) was chosen as the optimized WSP content to fabricate fiber-reinforced samples. In the subsequent step, glass fibers of 40 mm length and PP fibers of 12 mm length were used at 0.1, 0.2, and 0.4 wt%. Specimens were put in water (21 ± 2℃) for 27 days. Flexural and compressive strength tests were done on fiber-reinforced samples after 27 days.

Table 6.

Mix proportion of specimens containing perlite (weight percentage).

Mixture no	Cement (%)	Water (%)	Sand (%)	Coarse aggregate (%)	Waste stone powder (%)	Perlite (%)	Density (g/cm³)
CP	10	13.14	47.24	25.6	–	4.02	1.83
CSP	10	22.68	22.37	24.45	16.48	4.02	1.95

In the next step, perlite as a light aggregate was used to investigate density, flexural and compressive strength of modified samples. Table 6 shows the details of mix proportions used for samples fabricated with perlite. The maximum size of perlite aggregates was 9 mm. The chemical composition of perlite is shown in Table 7. Glass fibers (40 mm length) and PP fibers (12 mm length) were added to perlite-fabricated samples at 0.1, 0.2, and 0.4 wt%. In the same way, specimens were put in water (21 ± 2℃) for 27 days and after that flexural and compressive strength tests were done.

Table 7.

Chemical composition of perlite (weight percentage).

SiO₂	Al₂O₃	Na₂O₃	Fe₂O₃	CaO	K₂O	MgO	Density (kg/m³)
75.90	14.23	4.18	0.17	0.70	4.31	0.54	70

Results and discussions

Figures 3 and 4 show the flexural and compressive strength results of neat samples, i.e. fabricated without reinforcing fibers (see Tables 4 and 5).

Figure 3.

Flexural strength of specimens fabricated with and without WSP.

Figure 4.

Compressive strength of specimens fabricated with and without WSP.

According to Figures 3 and 4, using WSP in cementitious samples causes an improvement in flexural and compressive strength compared to those fabricated without WSP. It seems that WSP performs as a filler within the mixture. Consequently, the void content of the sample will be decreased as WSP is added to the mixture. Figures 5 and 6 show the broken cross-sections of C and CS4 samples. As can be seen, the void content of CS4 sample is more than that of C sample.

Figure 5.

The broken cross-section of C sample.

Figure 6.

The broken cross-section of CS4 sample.

Flexural strength modeling of fiber-reinforced cementitious composite

A famous theory about analysis of steel-reinforced concrete is “Equal Cross-Section and/or Transformed Area.” In this way, cross-section occupied by fibers is replaced with matrix, like the steel bars which are replaced by concrete [19]. Figure 7 shows this phenomenon in accordance with equal cross-section theory. This equal area $S_{new}$ can be also obtained from mechanics of materials and/or strength of materials following the formula [20,21]

S_{new} = (\frac{E_{f}}{E_{c}}) \times A_{f}

(1)

where E_f and E_c are fibers and cementitious composite modulus of elasticity, respectively. A_f is the whole fibers occupied cross-section. Therefore, new moment

I_{new}

of inertia can be calculated by formula [22]

I_{new} = I_{old} + ({TC}_{R} - n_{f} \times s_{f}) \times \sum_{i = 1}^{n_{f}} (d_{i} - \frac{h}{2}) 2

(2)

while n_f is

n_{f} = \sqrt{\frac{N_{f} - N'_{f}}{l_{c} / l_{f}}}

(3)

where N_f is number of fibers,

N'_{f}

is number of fibers that are not parallel with the composite axis, and l_c and l_f are composite length and single fiber length, respectively.

I_{old}

is moment of inertia of the neat sample, i.e. concrete with no reinforcing fiber. Herein, d_i is the distance from each fiber row of fiber to the edge of the cementitious composite; h is the composite cross-section height; x is the distance between two neighboring fibers in a row or a column; n_f is the number of rows and/or columns of fibers; s_f is the single fiber cross-section, and

{TC}_{R}

is the whole fibers transformed cross-section that can be calculated through the following formula

{TC}_{R} = \frac{E_{f}}{E_{c}} \times \sqrt{N_{f} - N'_{f}} \times s_{f}

(4)

Figure 7.

Equal cross-section theory applied to fiber reinforced cementitious composite.

On the other hand, according to the mechanics of materials it is clear that flexural strength of a mass under flexural loading is as follows

σ = \frac{M \times c}{I}

(5)

where M is the bending moment; c is the distance from neutral axis to the edge, and I is the moment of inertia of the composite. In the next step, a new parameter B_s was introduced to investigate the effect of fiber in cementitious composite. Consequently, cementitious composite flexural strength can be calculated as follows

σ = \frac{M \times c}{I_{new}} \times B_{s}

(6)

B_{s} = 1 + (\frac{n_{f}^{2}}{2} \times \frac{S \times μ_{c} \times α}{N'_{f} \times μ_{f} \times d_{f}})

(7)

According to Figure 8, all components below the neutral axis are under tension. Therefore, these fibers should be only considered in equation (7), i.e. fibers above the neutral axis are not efficient under compressive loading. That is why $n_{f}^{2} / 2$ of fibers have been used in equation (7). S is the single fiber lateral surface; μ_c is the coefficient of friction between fiber and matrix (concrete); μ_f is the coefficient of friction within fibers; and d_f is fiber diameter that is calculated by [23]

d_{f} = 4.44 \times 10 - 3 \times (\frac{T}{ρ_{f}}) \frac{1}{2}

(8)

where T is the Tex count of fiber and

ρ_{f}

is the fiber density. α is a parameter that can be obtained through

α = \sqrt{K \times (\frac{1}{E_{c} S_{c}} + \frac{1}{E_{f} S_{f}})}

(9)

where K is the slip modulus related to the geometrical properties of fiber and matrix; E and S are elastic modulus and cross-section area; meanwhile, the subscripts c and f correspond to concrete and fiber, respectively. It is clear that the fiber lateral surface is as follows

S = π d_{f} l_{f}

(10)

where l_f is fiber length. So, B_s equals to

B_{s} = 1 + (\frac{n_{f}^{2} \times π \times l_{f} \times μ_{c} \times α}{2 \times N'_{f} \times μ_{f}})

(11)

Figure 8.

A beam under flexural loading.

Table 8 shows the results of flexural parameters calculated for glass and PP fibers at different weight percentages. Herein, it is assumed that one-half of fibers are only paralleled with the main composite longitudinal axis.

Table 8.

The results of flexural parameters calculated for glass and PP fibers at different weight percentages.

Fibers (wt%)	N_f	$n_{f}$	$s_{f} (mm 2)$	${TC}_{R} (mm 2)$	$I_{new} (mm 4)$	M (N × m)	$B_{s}$	x (mm)
0.1 % glass	$67.5 \times 103$	92	$7.38 \times 10 - 9$	2.576 × 10⁻¹³	213333.335	26.8	1.0000000161	0.43
0.2 % glass	$135 \times 103$	130		3.64 × 10⁻¹³	213333.337	35.4		$0.3$
0.4 % glass	$270 \times 103$	184		5.152 × 10⁻¹³	213333.342	38.4		$0.21$
0.1 % PP	$112.5 \times 103$	66	$0.00636$	7.765 × 10⁻⁸	211073.984	25	1.0000000003	$0.51$
0.2 % PP	$225 \times 103$	93		1.094 × 10⁻⁷	208939.084	30.8		$0.34$
0.4 % PP	$450 \times 103$	131		1.154 × 10⁻⁷	204408.562	34.6		$0.21$

PP: polypropylene.

Figures 9 and 10 the show flexural and compressive test results of CS4 specimen containing PP and glass fibers.

Figure 9.

Flexural strength of CS4 specimen containing PP and glass fibers.

Figure 10.

Compressive strength of CS4 specimen containing PP and glass fibers.

In addition, Figures 11 and 12 show flexural and compressive strength test results of CP and CSP containing PP and glass fibers.

Figure 11.

Flexural strength of CP and CSP specimens containing glass and PP fibers.

Figure 12.

Compressive strength of CP and CSP specimens containing glass and PP fibers.

According to Figures 11 and 12, in samples fabricated with perlite, flexural and compressive strengths have been increased by using WSP compared to samples prepared without WSP.

It is clear from Figures 9 to 12 that glass and PP fibers reinforce the cement composite structure to resist during flexural loading. Furthermore, fibers prevent crack propagation in specimen during flexural loading and shrinkage. According to Figure 9, increase of weight percentage of fibers results in improving flexural strength. This result shows a complete consistency with the proposed model. According to equation (4), an increase in fiber content means an increase in total number of reinforcing fibers N_f which increase the transformed area TC_R to be greater. In addition, glass fibers increase the flexural strength of cementitious composites more than PP fibers. This is due to the reason that glass fibers have higher modulus of elasticity E_f compared to PP fibers (see equation (4)). According to Figure 10, fibers do not have a significant effect on compressive strength.

On the other hand, perlite existence in cementitious composite specimens decreases flexural and compressive strength. Since perlite surface is morphologically smooth in comparison with other components such as sand, it would be possible to decrease cohesion between matrix components, which leads to make porosity in cementitious phase. Using glass and PP fibers within samples containing perlite and WSP improves flexural strength more than samples just containing perlite. It seems that in specimen containing WSP, the friction between fibers and WSP increases the resistance against flexural loading compared to samples fabricated with perlite which has smooth surface.

Finally, an analysis of variance (ANOVA) and Duncan test were applied on output data at a 95% confidence level by using SAS 9.1 program. Tables 9 and 10 show the ANOVA results related to WSP and fiber attendance effects, respectively. As can be seen, both effects are valid at 95% confidence level.

Table 9.

ANOVA statistical analysis results for samples containing waste stone powder.

Source	DF	Sum of squares	Mean of square	F value	Pr > F
Model	3	2.76933104	0.92311035	69.66	<.0001
Error	8	0.10601909	0.01325239
Corrected total	11	2.87535013

Table 10.

ANOVA statistical analysis results for samples containing fibers.

Source	DF	Sum of squares	Mean of square	F value	Pr > F
Model	3	0.48707193	0.16235731	81.57	<.0001
Error	8	0.01592250	0.00199031
Corrected total	11	0.50299443

According to Tables 9 and 10, the large value of F proves the effects of WSP and fibers on composite strength. Tables 11 and 12 show the Duncan test results related to WSP within group effect and fiber attendance effect, respectively.

Table 11.

Duncan statistical analysis results for samples containing waste stone powder.

Alpha	0.05
Error degree of freedom	8
Error mean square	0.013252
Number of means	2	3	4
Critical range	0.2167	0.2259	0.2310
Duncan group	Mean	N	Treat
A	3.52067	3	w
B	3.12267	3	z
C	2.53833	3	y
D	2.29912	3	x

Table 12.

Duncan statistical analysis results for samples containing fibers.

Alpha	0.05
Error degree of freedom	8
Error mean square	0.00199
Number of means	2	3	4
Critical range	0.08400	0.08753	0.08951
Duncan group	Mean	N	Treat
A	2.29913	3	w
B	2.14520	3	z
C	1.97167	3	y
D	1.75800	3	x

According to Tables 11 and 12, Duncan test results show that each group of samples has different mean values, and adding WSP and fibers are effective on compressive strength.

Conclusion

Based on the results of experiments carried out in this study, the following conclusions can be obtained. Cementitious composite samples containing WSP have flexural and compressive strength more than samples without WSP at the same cement content. With increasing WSP weight percentage in cementitious composite samples, flexural and compressive strength increases too. WSP performs as a filler within the matrix to reduce the porosity and to bring more cohesive matrix. Using glass and PP fibers increases flexural strength of cementitious composite samples. The more the fiber content, the more flexural strength can be obtained. This result fits with the “modified equal cross-section theory” developed in this study. Fibers do not have a significant effect on compressive strength. Low-density cementitious composite was obtained by using perlite. Perlite decreases flexural and compressive strength of the composite. Using WSP with perlite increases flexural and compressive strength in comparison with specimens without WSP. Using glass and PP fibers within the cement matrix containing perlite and WSP increases flexural strength and does not have a significant effect on compressive strength.

To conclude, it is emphasized that WSP is an environmental problem. This paper suggests the use of WSP within the cement matrixes reinforced with glass and/or PP fibers, meanwhile fabricated with LWAs such as perlite. Using chemical water-proof resins such as polyvinyl alcohol to prevent swelling of cement-WSP based samples is an interesting research field in future works.

Footnotes

Funding

This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.

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