Study of the Characteristics of Kutai Kertanegara Local Quarry Stone for Self-Compacting Concrete Production

3.1 Physical properties of local aggregates

Based on the results of testing the physical properties of local aggregates, the specific gravity of Quarry 1 = 2.713, Quarry 2 = 2.645, Quarry 3 = 2.510 and Quarry 4 = 2.576 was obtained. The specific gravity of the four quarries has met the specifications of ASTM C 127 [18] and, according to Neville [22], is 2.50 - 2.80.

Based on the results of testing the mud content of local stone in the Quarry 3 quarry, the results were 0.867% and met ASTM C136 [25]. As shown in Table 2, Quarry 1, Quarry 2, and Quarry 4 did not meet the maximum permissible coarse aggregate mud content value of <1%.

The water content of the four quarries has met ASTM C556-89, with the permissible coarse aggregate water content value of 0 - 3%.

The aggregate absorption from 4 quarries did not meet the ASTM C127 [23] specifications, which state that the absorption value is 2% - 7%.

Table 2. Result of local aggregates physical properties

3.2 Classification and compressive strength of local rocks

Based on the aggregate wear test results on quarry 2 samples as shown in Table 3, a relatively large value of 34.72% was obtained, while quarry one samples had the smallest value of 29.48. The abrasion value on the aggregate is related to the compressive strength value. The greater the abrasion value produced, the lower the compressive strength value produced. The aggregate wear study from 4 quarries has met the specifications of <40%.

Table 3. Local rock abrasion

3.2.1 Mechanical properties of stone

After testing the physical properties of the stone samples before and after they were cut into 5 cm cubes, the mechanical properties of the stone were tested by conducting a compressive strength test.

3.2.2 Mechanical properties of 5 cm stone

After the stone was cut into a cube shape measuring 5 x 5 x 5 cm, the compressive strength of the stone was tested. So that it can be written using the formula according to SNI 1974-2011 [30].

Based on Table 4 From the results of the compressive strength of the rock that can be used as coarse aggregate for structural concrete with the SCC method is the location of Quarry 4, where its strength is greater than the compressive strength of concrete 50 MPa. For Quarry 3, the rock strength is between 30 - 50 MPa, so a typical concrete sample is made. While Quarry 1 and Quarry 2 have less than 30 MPa, no concrete samples are made because they will produce non-structural concrete (Less than 17 MPa) [37, 38].

Table 4. Compressive strength test of rock (5 cm Cube)

3.3 Regional geological conditions of local rock samples

Based on the regional geological map of the Samarinda sheet on a scale of 1:250,000, the location of rock sampling is in Quarry 3 and Quarry 4, including the Pamaluan formation (Figure 1). The Pamaluan Formation shown in Figure 2 is composed of quartz sandstone with inserts of claystone, shale, limestone, and siltstone that are very well layered. The research location and rock samples in the research conducted are sedimentary rocks that are identified as limestone [39]. The limestone based on the regional geological map has a gray color, is solid, has medium-coarse grains, has a layered structure in some places and contains large foraminifera fossils. The Pamaluan Formation is the oldest rock exposed on the Samarinda Sheet Geological Map, and the upper part of the Pamaluan Formation has a finger-like relationship with the younger rocks above it, namely the Bebulu Formation [40]. The thickness of the rock in this formation ranges from 2000 m, and the age of the Pamaluan Formation is Oligocene to early Miocene.

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Figure 2. Regional geological map of research area

Based on macroscopic observations, the limestone in the Quarry 3 and Quarry 4 samples is gray and solid, with a grain size generally in sand. The rock reacts with HCl, which indicates that the rock is composed of calcite minerals. In the rock samples, fractures are also filled with secondary calcite minerals. Petrographic analysis was carried out on two limestone samples, namely in the Quarry 3 and Quarry 4 samples, showing that the rock is composed of calcite minerals and tends to be massive. Cracks or fractures in the rock filled with secondary calcite minerals can also be observed in microscopic appearance (Figure 3). The presence of joints or fractures as discontinuity planes in the rock can be weak planes in the rock and reduce the strength of the rock [41].

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Figure 3. Results of microscopic analysis of limestone in samples (a) Quarry 3 and (b) Quarry 4

3.4 Comparison with rock samples from Palu

The rocks used as construction materials originating from Palu have different characteristics. Analysis shows that the stones are included in the type of igneous rocks, which, based on the IUGS classification, are called andesite [42]. Megascopically, the stones have a slight color, aphanitic texture (minerals are so minor that they cannot be observed directly), and massive structure. In microscopic observations, the andesite is entirely composed of minerals with a mineral composition predominantly plagioclase, pyroxene, and hornblende, and quartz minerals are present in smaller amounts (Figure 4.) Microscopic results of rock samples from Palu show that the rocks are andesite igneous rocks. Mineral composition: Pl: plagioclase, Px: pyroxene, Hb: hornblende, and Qz: quartz.

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Figure 4. Microscopic results of rock samples from Palu

3.5 Slump flow result

The slab for Quarry 3 concrete is obtained at 100 - 140 mm, according to the planned standard. Meanwhile, the slump flow for quarry 4 concrete ranges from 510 - 550 mm according to the SCC concrete standard.

3.6 Compressive strength of concrete

3.6.1 Local stone quarry 3

The average compressive strength of Quarry 3 aggregate concrete is 22.838 MPa as shown in Table 5.

Table 5. Standard deviation (Quarry 3)

∑Xi = Total compressive strength of test specimens

n = Lots of data

$\begin{gathered}\sum X i=342.567 \\ n=15 \\ \sum(X i-X)^2=605.260\end{gathered}$

Average compressive strength

$\begin{gathered}\bar{X}=\frac{\sum X i}{n} \\ \bar{X}=\frac{342.567}{13}=22.838\end{gathered}$

Standard Deviation (s)

$\begin{array}{r}s=\sqrt{\frac{\sum(X i-\bar{X})^2}{n-1}} \\ s=\sqrt{\frac{605.260}{14}}=6.575\end{array}$

Achieved compressive strength:

fc’ = $\bar{X}$ + (1.16 $\times$ s)

Upper limit fc'  = $\bar{X}+(1.16 \times s)$ = $22.838+(1.16 \times 6.575)$ = 30.465 MPa

Lower limit fc’ = $\bar{X}-(1.16 \times s)$ = $22.838-(1.16 \times 6.575)$ = 15.211 MPa

The average compressive strength of concrete is 22.838 MPa while stone is 42.05 MPa, with concrete strength achieved only 54.31% of the strength.

3.6.2 Local stone quarry 4

The average compressive strength of Quarry 4 aggregate concrete is 30.852 MPa as shown in Table 6.

Table 6. Standard deviation (Quarry 4)

Total compressive strength of test specimens

$\sum \mathrm{Xi}$ = 647.855

Lots of data, n = 21

Amount of data, $\sum(\mathrm{Xi}-\mathrm{X})^2$ = 593.129

Average compressive strength  ($\overline{\mathrm{X}}$) = 30.852

Standard Deviation (s) = 5.466

Achieved compressive strength:

Upper limit fc’ = $\overline{\mathrm{X}}+(1.08 \times \mathrm{s})$ = $30.852+(1.08 \times 5.466)$ = 36.733 MPa

Lower limit fc’  = $\overline{\mathrm{X}}-(1.08 \times \mathrm{s})$ = $30.852-(1.08 \times 5.466)$ = 24.970 MPa

The average compressive strength of concrete is 30.852 MPa while the stone is 64.89 MPa with the concrete strength achieved only 47.55% of the stone strength.

3.7 Development of concrete strength

Based on the concrete compressive strength data according to its age from Table 4 and Table 5, it is made into a strength development graph in Figure 5. The graph shows that the concrete experiences fluctuating strength development and generally experiences decreasing strength from 14 to 28 days. Meanwhile, for high-quality SCC concrete, its strength increases from 28 days to 56 days and decreases again at 90 days. Thus, the strength of this local stone concrete shows a decrease at 28 days for standard concrete and 90 days for high-quality SCC concrete. While the strength of concrete using ex-hammer stone shows that the development of concrete strength is increasing according to the increase in concrete age [22], this indicates that the local rock used does not meet the standard of concrete strength development. This condition is greatly influenced by the strength of the stone, which is the main element that forms the strength of concrete. Quarry stones 3 and 4 are types of limestone, and there are many fracture fields, so this stone is more accessible to break or split in concrete when receiving loads. In addition, the water for the cement hydration process at the age of 21 and 28 days begins to be partially absorbed by the stone, filling the fracture field so that the stone becomes weaker in strength. The variation in the condition of this stone makes the strength of the concrete low and fluctuates after the age of the concrete is 14 days.

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Figure 5. Concrete compressive strength development graph

3.8 Concrete collapse patterns

The collapse pattern generally forms columnar [30]. This condition is predominantly influenced by coarse aggregate and mortar. Following the sedimentary rock type with many weak areas, it first experiences destruction [41]. The development of concrete strength that decreases is influenced by rock fractures that absorb water from the concrete mixture so that over time, the fractures become weak and the weak areas become more extensive. The evidence causes 28-day-old concrete and 90-day-old high-quality SCC concrete to experience a decrease in strength, as shown in Table 7.

Figure 6 above shows that the coarse aggregate is more broken or split, which indicates the rock's lower strength compared to the strength of the mortar and the bond between the rock and the mortar. The strength of coarse aggregate is the main element that forms the strength of concrete. If the strength of the stone is low, it can significantly impact the concrete's strength and durability [22]. In addition, the strength of concrete depends on the physical properties of the coarse aggregate, where most of the concrete's volume is filled by the coarse aggregate, which can affect its performance [5].