Mechanical properties and microstructure of roller compacted concrete incorporating brick powder, glass powder, and steel slag

1.1 Literature review

In their study, Malkawi et al. [4] undertook a comparative analysis of various pozzolanic materials employed in the construction of roller-compacted concrete (RCC) dams. The researchers determined that natural pozzolanic materials and/or rock flour exhibited exceptionally favorable physical and chemical properties in comparison to fly ash and other pozzolanic materials. As a result, they concluded that the utilization of natural pozzolanic materials and rock flour in RCC dam construction is highly advantageous and effective

In their research, Shuhua et al. [5] examined the characteristics and microstructure of RCC incorporating a high volume of low-quality fly ash. The study demonstrated that the utilization of 60% ground fly ash in cement led to notably accelerated and enhanced property development compared to using an equivalent amount of untreated fly ash. The incorporation of a high volume (60%) of ground low-quality fly ash resulted in the refinement of pore size and improved pore size distribution within cement pastes. This substantial improvement in microstructure consequently elevated the strength and durability of the RCCs.

In their investigation, Lam et al. [6] explored the influence of compaction delay on the optimal moisture content and mechanical properties of roller-compacted concrete pavement (RCCP) incorporating electric arc furnace (EAF) Slag Aggregate. The study revealed that the higher water absorption characteristic of EAF slag, which typically leads to a decrease in water content, was effectively mitigated by employing a novel mixing method. Surprisingly, the delay in compaction had minimal impact on the optimal water content and maximum dry density of RCCP. Additionally, the compressive strength and splitting tensile strength of RCCP utilizing EAF slag aggregate met the strength requirements for pavement, even when compaction was delayed by up to 90 min.

In their study, Fardin and Santos [7] aimed to examine the mechanical and physical characteristics of RCC by incorporating recycled concrete aggregate (RCA) as a replacement for natural coarse aggregate. The research revealed that as the proportion of RCA in the mixtures increased, there was a decrease in specific mechanical properties, notably the modulus of elasticity. However, it was observed that there was no significant decrease in the splitting tensile strength, indicating that the utilization of RCA as a substitute for natural coarse aggregate in RCC did not adversely affect this particular strength parameter.

1.1.5 Cementitious materials

This study incorporated two types of waste materials: Waste glass powder (WGP) and waste brick powder (WBP). To attain a fineness comparable to that of cement, these materials underwent several phases of preparation and grinding

The waste materials (glass and brick) were obtained from local landfills and construction sites in Mosul, Iraq. The collected waste was thoroughly washed and air-dried. Subsequently, each material underwent separate grinding for approximately 1 h using a Los Angeles abrasion machine, as depicted in Figure 1, following the guidelines outlined in ASTM C131 [11].

Figure 1

Los Angeles machine.

Then, it was passed through sieve No. 4 and the materials from the sieve were ground in another mill, Guyixuan (MFS 150), Figure 2.

Figure 2

Guyixuan (MFS 150) grinding machine.

The test results demonstrated that the fineness of the material met the requirements specified in ASTM C 618 [13]. The specific gravity of the prepared powder was determined following the procedures outlined in ASTM C188 [12]. Chemical analysis of these materials was conducted at Soran University in Soran, Erbil, Iraq, utilizing sequential X-ray fluorescence. The results of these tests are presented in Table 7.

Table 7

Physical properties and chemical compositions of WGP and WBP

Physical properties	Values		ASTM C618 [13]
	WGP	WBP
Specific gravity	2.56	2.73	—
Blaine´s fineness (cm²/gm)	2,980	3,600	—
Retained on sieve No. 325 (%)	24	20	≤34

Chemical composition	Content%		ASTM C618 [13]
SiO₂	72.7	51.9	—
Al₂O₃	1.49	13.5	—
Fe₂O₃	1.17	4.5	—
CaO	11.9	15.6	—
SO₃	0.33	3.43	≤4
MgO	1.48	6.3	—
Alkalis (Na₂O + K₂O)	8.9	2.8	—
MnO	0.014	0.122	—

2.1 Procedure for determining the mixture proportions of reference mixtures

1. Select well-graded dry coarse and fine aggregates that fall within the prescribed limits of ACI 211.3R (2002).

2. Determine the optimum moisture content and maximum dry density using ASTM D 1557.

3. Determine the optimum moisture content (OMC) and maximum dry density of RCC mixtures by casting various quantities of cement, ranging from 10–17% of the dry aggregates’ mass. For each cement content, four mixtures were cast, with varying water content ranging from 3–9% of the dry aggregate’s weight, The OMC for cement contents of 10, 13, 14, and 17% resulted in values of 6.23, 6.86, 7.1, and 8.56%, respectively. Figure 3 illustrates the moisture vs density curves for the 14% cement content mixture.

4. Four RCC mixtures were cast using cement content of (10, 12, 14 and 17) as percentage of aggregate content. by fixing optimum moisture content determined from stage 2 saving as the water quantity for the mixture. The compressive strength and flexural strength of each mixture were measured after 28 days. Based on the desired flexural strength range of 4–5 MPa, a cement content of 14% was selected, which was used for casting all the mixtures discussed in this work.

5. To meet the desired strength requirements, a mixture proportion of 1:3.23:2.63, w/c = 0.47 was used as reference mixture (R0).

2.2 Procedure for determining the mixture proportions of GRCC

1. Mixtures R1–R4 were prepared by incorporating brick powder (BP), ranging from 10–40% as replacement of cement content.

2. Mixtures R5–R8 were prepared by incorporating glass powder (GP), ranging from 10–40% as replacement of cement content.

3. Mixtures R9–R12 were prepared by incorporating steel slag (SS), ranging from 10–40% as replacement of cement content.

Table 8 presents the detailed composition of the mixtures used in this work.

2.3 Sample preparation and curing process

During this stage, the procedure involved the preparation of mixture specimens followed by their curing in tap water for durations of 7 and 28 days. For assessing compressive strength, a total of six plastic cube molds (100 × 100 × 100 mm) were utilized for each mixture. These cubes were poured in two layers and compacted using a vibrating hammer, as depicted in Figure 4. At the age of 7 days, three cubes were examined, while another set of three cubes was tested at 28 days, all within tap water conditions. Additionally, to evaluate the flexural strength, three plastic prism molds (100 × 100 × 400 mm) were filled for each mixture. Similar to the cube molds, the prism molds were poured in two layers, compacted with a vibrating hammer, and tested after 28 days of curing.

Figure 4

Vibrating hammer for molding RCC samples.

2.4 Sample testing procedures

2.4.1 Compressive test

The compressive test involved subjecting (100 × 100 × 100 mm) cube specimens to compression after curing in water for (7 and 28) days. A compression testing machine with a loading rate of 0.3 MPa/s and a capacity of 2,000 KN, as depicted in Figure 5, was used for this test. The testing procedure followed the guidelines outlined in BS: 1881: Part 116: 1983 [14].

Figure 5

Compressive strength test: (a) cube specimen and (b) compressive testing machine ready to test the cube.

2.4.2 Flexural test

Flexural test was performed on prisms (400 × 100 × 100 mm) using simple beam with third-point loading according to ASTM C78 [15]. A universal testing machine with a loading rate of 0.3 MPa/s and a capacity of 2,000 KN, as depicted in Figure 6a and b, was used.

Figure 6

Flexural strength test: (a) prism specimen and (b) flexural testing machine ready to test the prism.

2.4.3 Vibrating hammer

The samples were produced using a vibrating hammer in accordance with ASTM C1435 [16]. Figure 7 illustrates the vibrating hammer employed to prepare all RCC samples, adhering to the specifications outlined in ASTM C1435.

Figure 7

Vibrating hammer for preparing RCC Samples.

3.1 Strength activity index (SAI)

The activity index test was employed to assess the activity of the materials employed, with a 20% replacement ratio utilizing various waste materials like glass, stainless steel, and BP, as per ASTM C311 [17]. The SAI exceeded 75% after 7 days. Eq. (1) was utilized to calculate the SAI.

where, z is the mean compressive strength of the pozzolanic materials, and R is the average compressive strength of the reference mixture.

The SAI for WBP, WGP, and waste steel slag (WSS) was determined by comparing them with the reference mixture (R0) at 7 and 28 days. The corresponding results are depicted in Figure 8.

Figure 8

SAI for 20% replacement of WBP, WGP, and WSS.

Based on the aforementioned findings, the Substitution Activity Index (SAI) surpassed 75%. This indicates the presence of the desired pozzolanic property in these materials. Consequently, they are deemed appropriate for substituting cement in concrete mixtures.

These results align with previous studies [18,19,20], corroborating their findings.

The observed activity can be attributed to the reaction between the SiO₂ present in WBP, WGP, and WSS, and the calcium hydroxide produced during cement hydration [21]. This reaction leads to the formation of secondary calcium silicate hydrate (C–S–H) [23]

Additionally, the findings indicate that WSS exhibits a higher SAI compared to the other materials. This can be attributed to the higher fineness and specific surface area of WSS powder in comparison to the others. The elevated specific surface area enhances the contact area, thereby increasing the effectiveness of its pozzolanic properties [22]

3.2 Compressive strength test results

Table 9 and Figure 9 display the results of RCC mixtures/ compressive strength.

Figure 9

Compressive strength test results.

Table 9 and Figure 9 show that the inclusion of waste materials cause a diminution in compressive strength at both 7 and 28 days as compared to reference mixture.

Table 9 and Figure 9 also show that at 7 days, compressive strength of 20% replacement of cement by BP (R2) is greater than that of 20% replacement of cement by SS (R10), while beyond 28 days, the strength development rate was found to be higher in SS (R10) when compared with (R2) mixture.

The findings demonstrate that the proportion of SS and the duration of the curing process had a moderate impact on the development of compressive strength. The glossy constituents present in SS exhibit a gradual reaction with water.

Based on the findings, it was observed that the compressive strength increased from 7 days to 28 days. Furthermore, the mixes incorporating WSS exhibited higher compressive strength values compared to the mixes containing WBP or WGP at the same replacement ratio. This difference can be attributed to the pozzolanic effect of SiO₂ on calcium hydroxide, leading to the formation of secondary calcium silicate hydrate (C–S–H) [23].

By enhancing the specific surface area of WSS, the contact area is enlarged, resulting in heightened consumption of calcium hydroxide and improved pozzolanic effectiveness. Additionally, this process contributes to denser microstructural formation, ultimately enhancing resistance [22,23,24].

3.3 Flexural strength test results

Table 10 displays the results of RCC mixtures’ flexural strength.

According to the information presented in Table 10, it is evident that the incorporation of waste construction materials (WBP,WGP, and WSS) leads to a decrease in the flexural strength of GRCC in comparison to the reference mixture. This finding aligns with prior studies [18,22,24].

Furthermore, it is noteworthy that “R2 and R6,” which include WBP and WGP, exhibit reduced flexural strength compared to “R10,” which incorporates WSS at the same replacement percentage. This disparity can be attributed to the higher specific surface area of WSS in comparison to WBP and WGP. Consequently, finer particles necessitate a greater amount of water, resulting in increased water consumption [14].

4.1 XRD

The outcomes of XRD analysis of the reference mixture and the GRCC samples are shown in Figures 10–13, respectively.

Figure 10

XRD pattern for reference mixture at 28 days in tap water.

Figure 11

XRD pattern for green mixture containing 20% WBP at 28 days in tap water.

Figure 12

XRD pattern for green mixture containing 20% WGP at 28 days in tap water.

Figure 13

XRD pattern for green mixture containing 20% WSS at 28 days in tap water.

The XRD analysis of the selected GRCC samples reveals similar peaks with varying intensities for the main phases, namely, quartz, calcite, and graphite 2H. Among these phases, quartz exhibits the majority of the peaks observed.

4.2 SEM

Figures 14–17 show the SEM morphology of reference mixture and the GRCC, respectively.

Figure 14

SEM image of reference mixture.

Figure 15

SEM image of green mixture containing 20% WBP.

Figure 16

SEM image of green mixture containing 20% WGP.

Figure 17

SEM image of for Green mixture containing 20% WSS.

From Figures 14–16, the generation of C–S–H can be seen, which is a product of secondary hydration reactions. Also, a small amount of calcium hydroxide Ca(OH)₂ can be seen.

Figure 16 also shows that in the mixture incorporating WSS, it was observed that the calcium silicate hydrate (C–S–H) was denser when compared to the mixtures containing WBP or WGP at the same replacement ratio. This difference can be attributed to the pozzolanic effect of SiO₂ on calcium hydroxide, leading to the formation of secondary calcium silicate hydrate (C–S–H) [23].

The microscopy analysis substantiates the findings and conclusions derived from the compressive strength, density, and other mechanical testing.

5.1 Recommendations for further work

1. Conduct additional durability tests: Explore the durability characteristics of GRCC, such as resistance to freeze–thaw cycles, chemical exposure, and wetting and drying cycles.

2. Investigate alternative reinforcement materials: Explore the use of alternative reinforcement materials, such as fiber-reinforced polymers (FRP) or carbon fibers, to enhance the mechanical properties and durability of GRCC.

3. Explore sustainable production methods: Investigate eco-friendly production methods for GRCC, such as incorporating recycled aggregates or optimizing energy consumption during the manufacturing process, to enhance the sustainability of the material.