Effect of Silica Fume on Some Properties of No-Fine Concrete with Recycled Coarse Aggregate

N o-fines Concrete is a lightweight porous concrete produced by omitting sand from the traditional concrete mix. It helps replenish the groundwater aquifer by directly allowing precipitation to seep into the earth thanks to its wide pores. This work studied the influence of partially replacing cement with silica fume (SF) with percentages of 5, 8, and 10% on some properties of no-fine concrete made using recycled coarse aggregate. The natural coarse aggregate (NA) was replaced with 10%, 20%, and 30% by crushed reactive powder concrete waste volume as recycled aggregate (RA). The optimum percentage was 10% RA with 10% SF, which indicated a substantial improvement in the no-fine concrete's strength, dry density, and water absorption compared to the design mix. The results exhibit increases in percentages in compressive strength, tensile strength, flexural strength, and dry density by 18%, 14%, 16%, and 1%, respectively, while exhibiting a decrease in water absorption by 5% at 28 days.


INTRODUCTION
No-fines concrete (NF) is a kind of lightweight concrete that consists only of cement, water, and coarse aggregate, excluding fine aggregate.This concrete type is called pervious, porous, or zero-fine concrete.The aggregate is typically a single size and held together with cement paste.Thus, large particles accumulated, each coated in a 1.3 mm cement paste layer.This type of concrete has more voids than normal concrete, resulting in a much lower strength.It has been employed in a variety of applications, particularly pavement.The interior and exterior walls of buildings are frequently made with no-fine concrete.No-fine concrete is also utilized in insulation and partition construction.NF can be used as rural road pavement with a design load of three tons.Furthermore, it could be used as a sub-base material in rigid or flexible pavements (Alam et al., 2014;Salih and Fidel, 2016;Jiahao et al., 2019;Pradhan and Behera, 2022).Materials that have been recycled are now favoured in construction as a replacement for aggregates because of their environmental benefits.From both an environmental and economic standpoint, recycled aggregate is superior to natural aggregate.An enormous amount of waste material would be produced by demolishing old reinforced concrete structures, posing a major environmental threat.The ideal solution to deal with the issue of waste concrete is to recycle a significant amount of it, specifically by employing recycled coarse aggregate concrete technology.The recycled aggregate quality exhibits significant variation based on the source concrete from which it is generated, such as water absorption, and as a result, affects the concrete properties Silica Fume has already been acknowledged as a pozzolanic additive that effectively improves concrete's chemical durability and mechanical characteristics.SF is a byproduct substance that reduces waste.In the ferrosilicon and silicon industries, the smelting process provides non-crystalline silica.It can be used as a mixture at the concrete mixer, as packed powders or a slurry, or even as a factory-blended cement component.The utilization of SF has the potential to decrease cement consumption, thereby reducing CO2 emissions The study employed the equivalent volume method to substitute cement with varying levels of SF (3%, 6%, 9%, and 12%).The results showed that the inclusion of SF had a notable positive impact on the durability and strength of previous concrete, particularly in terms of its resistance to freeze-thaw cycles.Employing the equal volume replacement technique resulted in small changes to the permeability and porosity of all previous concrete mixes, with variations in the SF content.(Galishnikova et al., 2020) investigated the impact of incorporating RA as a substitute for NA in previous concrete at varying proportions from 0% to 100% with an increment of 25%.Additionally, the influence of introducing 5% and 10% of SF as a cement substitute on the characteristics of previous RA concrete was examined.The results demonstrated that a reduction in the characteristics of concrete occurred when the proportion of RA increased.The inclusion of SF resulted in a development in mechanical characteristics.It was described that the inclusion of 5% SF into concrete containing 50% RA increased by 5.5% and 4.2% in the density of hardened and fresh pervious concrete, respectively, and increased compressive, tensile, and flexural strengths by 100, 20, and 20.3%, respectively, at 28 days.(Bhutta et al., 2013) inspected the use of RA in producing porous concrete with appropriate strength and permeability.Styrene butadiene rubber-based re-dispersible polymer powder and latex were added to improve the strength characteristics of the mixtures.When RA was used instead of natural aggregate, the compressive strength of the porous concrete was reduced.However, polymer modification greatly enhanced the compressive strengths employing regular and RA by 57 and 79%, respectively.This study examines the influence of using SF in the proportion of 5, 8, and 10% as a partial substitution of cement in NF with RA.The RA employed was demolished waste reactive powder concrete as a partial replacement of NA in the proportion of 10, 20, and 30 % to choose the optimum percentage.The characteristics examined in this study were compressive strength, tensile strength, flexural strength, dry density, and water absorption.

Cement
Ordinary Portland cement grade 32.5R was employed in this study under the brand name Al-Mas.The chemical and physical characteristics exhibited in Tables 1 and 2. have been according to the Iraqi Specification (IQS No.5, 2019).

Mix Design, Specimens, and Tests
Seven different mixes were prepared for this study after several trail mixes: the reference mix, three mixes where recycled demolished concrete aggregate was added in percentages of 10, 20, and 30% to replace the NA by volume, and three mixes in which SF replaced cement in three percentages of 5, 8, and 10% by weight and contained RA after choosing the best percentage of coarse aggregate replacement.The cement-to-aggregate ratio was 1:4 by weight; the cement weight was 275 kg/m 3 The w/c was 0.30, and the SP dose was 0.1% by the cement's weight, which improved the workability of the mixes with RA and SF and kept a constant w/c of 0.3.Table 7. Presents the mixes details.Following are the steps that were taken to mix the materials with a 0.1 m 3 capacity mixer: First, the interior of the mixer had been moistened and cleaned before use.The required amount of natural coarse aggregates was placed within the mixer and the half-required water and blended for a minute.The cement was placed inside the mixer with the remaining amount of water, and it continued to run till the cement paste had well covered the coarse aggregate and a homogeneous mixture had been produced.The same procedure was used to prepare mixes with RA and SF, except that the RA was blended with the natural aggregate, the SF was blended with the cement, and the SP was added to the water.The mixture was cast in oil-metal cylinders (100×200) mm, prisms (80×80×380) mm, and cubes (100×100×100) mm in layers and compacted with simple rodding, and it was conforming to (ASTM C192/C 192M, 2019).Subsequently, Table 7. Mixes detail the molds were covered with nylon and left for a day.The samples were de-molded and kept in curing tanks up to the testing date.

Compressive strength (CS)
Table 8. and Fig. 4 show RA and SF's impact on the NF's CS.The results exhibit that the utilization of RA decreased the CS, resulting from the weak aggregate characteristics of demolished concrete, which reduced the CS of NF.The best percent of replacement was 10% by volume, which exhibited the lowest loss of CS by 11% at 28 days compared to the design mix.On the contrary, using SF as a substitute for cement in mixes containing 10% RA enhanced the CS of NF.The best proportion of SF was 10%, which caused the increase of CS by 18% at 28 days compared to the design mix.This is due to the high SF particle fineness.Despite their greater surface area, SF particles will fill the holes in the no-fine concrete during mixing and compaction.As a result, a more densely packed structure with fewer porosity forms, increasing the concrete strength, which is compatible with (Jagan and Neelakantan, 2021).Table 9. and Fig. 5 show how RA and SF affect the TS of NF.The results showed that TS decreased with the employment of RA.The best percentage of the replacement was 10% by volume, which led to a 13% decrease after 28 days compared to the design mix.The utilization of SF as a weight substitute for cement with 10% recycled aggregate, on the contrary, increased the TS.The best percentage was 10%, which caused the increase of TS by 14% at 28 days compared to the design mix.This improvement is due to the development of concrete's microstructure, which is compatible with (Mirza and Saif, 2010).Table 10.and Fig 6 .demonstrates the impact of RA and SF on the FS.The results showed that FS declines when RA is used.The best percentage of RA was 10%, which showed a reduction of 9% at 28 days in comparison to the design mix.On the contrary, the employment of SF as a substitution of cement by weight with 10% RA increased the FS.The ideal percentage was 10%, which showed an increase in FS by 16% at 28 days compared to the design mix.Since FS and CS are directly related, concrete with the highest CS should also have the highest TS.Using SF to improve CS will produce a similar relative rise in FS also duo to SF's strong pozzolanic activity.This behavior is consistent with (Abubaker and Ghanim, 2022; Shafieyzadeh, 2015 ).11 and Fig. 7 show the influence of RA and SF on the dry density at 28 days.The results showed that the dry density declined when RA is used.The best proportion of RA is 10%, showed a reduction of 2%.This can be attributed to a low density of RA.The results also exhibited that the employment of 10% SF increased the density of no-fine concrete with 10% RA by 1% compared to the reference mix.The increase in density with SF is due to the high concentration of amorphous silica in SF and its reaction with the cement lime, creating a denser concrete microstructure

Water Absorption
Table 12. and Fig 8 .show the effect of RA and SF on water absorption at 28 days.The results show that the absorption increased when RA was used.The best proportion of RA was 10%, which showed the least increase in absorption by 12% compared to the reference mix.This increase in absorption might be explained by a rise in voids in the mix with RA compared to that with natural aggregate.The results also exhibit that utilizing SF in the NF mixes with 10% RA decreases the water absorption; when using 10% silica fume, the water absorption decreased by 5% compared to the reference mix.This is because SF has smaller particles, making the concrete denser.Generally, SF reduced pore size, which decreased water absorption.This behavior is consistent with (Sharaky et al., 2019).

CONCLUSIONS
The study investigated the influence of SF substituting 5, 8, and 10% of the cement weight in no-fine concrete with RA.Based on the results of the sample tested, the following conclusions can be drawn: 1) When RA was used in place of the equal volume of natural coarse aggregate, the CS, FS, TS, and dry density of no-fine concrete decreased while the water absorption increased.
2) The best percent of RA replacement was 10%, which exhibited the least reduction in CS, FS, TS, and dry density by 11, 9, 13, and 2%, respectively, and the least increase in water absorption by 12% concerning the reference mix. 3) Using 10% SF with 10% RA increased the CS, FS, TS, and dry density by 18, 16, 14, and 1%, respectively, while decreasing the water absorption by 5% compared to the reference mix.

(
Galishnikova et al., 2020; Jain and Pawade, 2015; Imam et al.,2018).Various researchers did several investigations to study the characteristics of no-fine concrete.(Liu et al., 2018) investigated how SF influences the characteristics of environmentally friendly previous concrete.

Figure 4 .
Figure 4.The influence of RA and SF on the compressive strength

Figure 5 .
Figure 5.The influence of RA and SF on splitting tensile strength

Figure 6 .
Figure 6.The Influence of RA and SF on Flexural Strength

Figure 7 .
Figure 7.The influence of RA and SF on dry density

Table 1 .
The chemical properties of cement

Table 2 .
The physical properties of cement The characteristics of the coarse aggregate employed in this study are demonstrated in Table3.
The coarse aggregates utilized in this study were NA from the Al-Nibaai quarry and RA from demolished waste reactive powder concrete, as shown in Fig.1.Both were single-sized and per Iraqi specifications (IQS No.45, 1984).

Table 3 .
The properties of coarse aggregate Figure 1.Demolished reactive powder concrete aggregate 2.1.3Silica fume The SF utilized in this study is illustrated in Fig. 2. Its properties are presented in Table 4.It complies with ASTM C1240-20 (ASTM C1240, 2020).

Table 4 .
Typical SF properties At 25°C Figure 2. SF used in the mixes 2.1.4MixingwaterThe water employed in this study conforms to Iraqi Specification No. 1703/2018 (IQS No. 1703, 2018), and its properties are shown in Table5.

Table 5 .
Mixing water properties

Table 6 .
Technical Properties of BETONIC-1030 SP* *according to the manufacturer

Table 8 .
The results of compressive strength

Table 9 .
The splitting tensile strength results

Table 10 .
The flexural strength results

Table 11 .
The dry density results Mix No. Dry Density (kg/m 3 ) Mix No. Dry Density (kg/m 3 )

Table 12 .
The absorption results Figure 8.The influence of RA and SF on water absorption