Reducing the Reactive Powder Concrete Weight by Using Building Waste as Replacement of Cement

The ability of reducing the high weight of reactive powder concrete (RPC) by decreasing the cement content using waste demolished building material to produce the eco-friendly sustainable RPC was the main goal of the experimental lab investigation. The collecting, crushing and grinding to high fineness powder waste of clay brick, win - dow glass and terrazzo tile constituted the best way to dispose without the need for a waste sanitary landfill. Nine RPC mixtures with 5, 10 and 15% partial replacement of cement weight in addition to control mix were prepared to investigate the strength. The slight enhancement strength of the RPC containing 5% of very fine powder clay brick or window glass or terrazzo tile as cement weight replacement cement up to (4.9, 4.2, 4.5)% – brick, (2, 1.8, 1.6)% – glass and (1.5, 0.5, 0.8)% – tile for (compressive – flexural – tensile), respectively, at 28 days compared to the control mix. The percentage of 10% still yielded acceptable strength results, while 15% presented the starting of reduction of (compressive – flexural – tensile) strength.


INTRODUCTION
The reactive powder concrete (RPC) is a developed concrete considered as a composite materials with a high strength and good durability [Liu et al, 2019]. It consists of cement, silica fume and very fine sand where the microstructure is improved of all particles in the mix to produce maximum density [Khitab et al, 2022]. The presence of the short length fibers significantly recovers the quasi-brittle characteristics and tensile damaging capability of the concrete [Singh, 2017;Mishra et al, 2017].
Producing cement is responsible for approximately 8% of global CO 2 emissions, so the ability of reducing cement content in concrete led to reduced pollution and produced a green concrete which defined as a form of eco-friendly concrete that is manufactured using waste or residual materials from different industries, and requires less amount of energy for production. Compared to traditional concrete, it produces less carbon dioxide, and is considered cheap and more durable [Suhendro, 2014;Al-Mansour, 2019;Sivakrishna, 2020]. The transformation of the building demolition waste to fine powder can be done by serial steps: collecting, separating, and crushing, finally grinding to powder in order to use as partial replacement of cement content. The reclaimed natural pozzolan can be used in concrete production where cementitious or pozzolanic action, or both, is desired [Al-Anbori and Al-Obaidi, 2016; Qasim, 2021]. The pozzolanic action can be beneficial, since the development of strength can be gained, and with high fineness rich cement paste micro-structure can be significant [Shannag and Yeginobali, 1995;Shannag, 2000;Ahmad, 2022]. It is necessary to consider the chemical and physical requirements presented in ASTM C 618 for class N [ASTM C618, 2017], and its ability to improve the fresh and mechanical properties especially at late ages, which increase along with particle size fineness that improve its effectiveness chemical reaction with cements silicates hydration (Ca(OH) 2 ) producing a good gel quality [Abdullah et al, 2022;. The main goal of the investigation focused on two parts: disposing of the demolition waste by cycling and using in construction projects and reducing the RPC cost by decreasing the high content of cement, thus producing sustainable RPC with less environment pollution from cement manufacture and waste sanitary landfill.

MATERIALS AND MIX DESIGN
The mixture composition of the RPC were:  Table 2.
• Fume silica conforming the ASTM C 1240 [ASTM C1240, 2015] presented in Table 3. • Straight steel fiber with aspect ratio = 65 presented in Table 4 Table 5. • Preparing recycled west demolished powder ( Figure 1). • The adoption mix design listed in Table 6 after many trials according to the works by   The adoption mix design listed in Table 6 after many trials according to the works by  as well as Al-Hassani et al. [2015].

PREPARATION OF SPECIMENS AND EXPERIMENTAL LAB TESTS
The mixing of material was as recommended by Khreef     The process of the curing cycle was based on experience [Al-Hubboubi and Abbas, 2018; , the local electricity conditions, and many trials of the curing cycle. Comparison between normal curing and cycle process was carried out till the adoption of curing cycle recommendation with percentage increase in compressive strength of more than 15% compared to standard curing (under water in lab). All details of the procedure described above and curing cycle are shown in Figure 2.

EXPERIMENTAL LAB TEST RESULTS AND DISCUSSION
The lab test results for compressive strength at 7, 28 and 90 days for control mixture and all other RPC using very fine powder waste materials (clay brick, window glass, terrazzo tile) as partial cement weight replacement by (5, 10 and 15)% are as shown in Figure 3. The percentage increase or decrease for the mixture containing demolition waste compared to control mix at 28days is presented in Figure 4. The use of brick powder for 5% and 10% achieved an improvement in mechanical strength and the use of 15% yielded a slight decrease (1.1%), so the use of BP is very encouraging for its very fine cementitious filling material micro-structure of concrete and pozzolanic chemical reaction between silicates hydration of cement [Ca(OH) 2 ] and active silica of BP to form essential densification filling gel  Compressive results for all mixes at different ages so still 5% gave better strength results than 10%, while 15% replacement led to a start of reduction strength (compressive, flexural, tensile) and that may be attributed to particle shape, activity and cementitious properties . The 5% of terrazzo tile powder replacement of cement can be used with slight increase of strength of RPC mixture, when increasing to 10% or 5% the retardation of mixture was pronounced and that can be attributed to the effect of second layer of mortar and to the highly contaminated of terrazzo tile to old mortar bonding. That led to lower benefits of high fineness and activity silica in raw materials form. The flexural and tensile strength results at 7, 28 and 90 days presented in Figures 5, 6 and 7, respectively, showed a compatibility and homogeneity of results with compressive strength, since whenever compressive strength increase or decrease, the flexural and tensile strengths also follow the same trend and that supports the confidence of results, as presented in Figure 8 with statistical linear equation for all ages and high R2.
Finally, the use of 5% waste demolition recycled powder as clay brick, window glass and terrazzo tile showed the highest improvement in mechanical strength, so the 5% was the most safe recommendation replacement by weight of cement in RPC mixture. In turn, 10% also can be used carefully, since its result close to control mix.

CONCLUSIONS
The improvement strength of the RPC containing 5% of very fine powder waste materials (clay brick or window glass or terrazzo tile) as partial replacement of cement weight up to (4.9, 4.2, 4.5)%, (2, 1.8, 1.6)% and (1.5, 0.5, 0.8)% for (compressive -flexural -tensile), respectively, using B, G and T, respectively, at 28 days was achieved compared to the control mix. The 10% replacement of brick powder can show development in strength around 3% at 28/days, and slight enhancement around 1% for glass powder, while the results start to decrease slightly around 1% for tile powder. The 15% replacement showed a reduction in the strength of RPC mixture for all waste mixture, especially for tile powder. The 10% replacement of cement weight can be more effective to reduce cement consumption and dispose of more demolition waste materials with acceptable strength of the RPC. The efficiency of the adoption of curing cycle with percentage increase in compressive strength of more than 15% at 28 days was achieved for control mix.