Experimental and Theoretical Study of a New Technique for Mixing Self-Compacting Concrete with Marble Sludge Grout

Prince Sattam Bin Abdulaziz University, College of Engineering, Civil Engineering Department, Alkharj, Saudi Arabia University of Carthage, Polytechnic School of Tunisia, Laboratory of Systems and Applied Mechanics, Tunis, Tunisia Higher Institute of Technological Studies of Sfax, Department of Civil Engineering, Sfax, Tunisia University of Sfax, Faculty of Science of Sfax, Georessources, Materials, Environment and Global Change Laboratory, Sfax, Tunisia University of Tunis El Manar, National Engineering School of Tunis, Civil Engineering Laboratory, Tunis, Tunisia


Introduction
Marble is a metamorphic rock resulting from the transformation of pure limestone [1].Waste marble powder is an inert material which is obtained as an industrial byproduct during sawing, shaping, and polishing of marble and causes a serious environmental problem [2]. is powder should be inactivated properly without polluting the environment.e most suitable inactivating method nowadays is recycling because it provides some advantages such as protecting the natural resources, energy saving, contributing to economy, decreasing the waste materials, and investing for the future [3].
Recycling of waste powders in concrete is a promising option for clean environment.Several researchers studied the incorporation of marble powder into cement-based products such as normal concrete, high-strength concrete, and self-compacting concrete.
e marble powder materials can be successfully and economically utilized to improve some properties of fresh and hardened self-compacting concrete [4].
e effects of substitution of cement with marble powder on the rheological and mechanical properties of self-compacting mortar (SCM) and self-compacting concrete (SCC) were studied [5][6][7][8][9][10]. e results indicate an improvement in the workability and the compressive strength of SCC with the use of marble powder.e marble powder was also used as an additive material in blended cement [11]. is cement has been obtained by intergrinding marble powder with Portland cement clinker at different blend ratios.Obtained results indicate that adding 10% of marble powder provides cement that conforms to EN 197-1 standard [11].
In addition, the marble powder was also used in concrete production, as partial replacement of Portland cement [3,[12][13][14][15][16]. e results show that the optimal replacement level of Portland cement by marble powder was found at 10% [12].
In general, grout must be characterized by four essential properties: the penetrability, the stability, the mechanical characteristics, and the durability.
e two main parameters influencing the grout penetrability are the granularity of its solid phase and its rheological characteristics (fluidity).e penetrability of the grout is also strongly influenced by the rheological properties of the grout.In particular, the fluidity must be such that the grout penetrability can be achieved so as not to degrade the granular structure.
is experimental and theoretical study is a continuation of our work on the valorization of marble waste [17]. is work focuses on the direct incorporation of marble sludge in self-compacting concrete in order to avoid the technical disadvantages for obtaining a marble powder: grinding after drying which require a lot of energy.
e first part of this work needs the study of the rheological behavior of MSG as a function of the added water amount.For this, different grouts were prepared and tested by varying the water/sludge ratio.In the second part, four self-compacting concretes (SCC) were mixed with grouts having different water/sludge ratios in order to validate a new technique of gassing self-compacting concrete with MSG.

Marble Sludge.
e chemical analysis of marble sludge, performed with an atomic absorption spectrometry "AAS" according to the requirements of EN ISO 15586 [18], is presented in Table 1.e results show that the marble sludge is too rich in calcite (CaCO 3 � 93.30%), and it is devoid of all clay and organic matter [19]. is last result was confirmed by the result of the methylene blue test, performed according to the requirements of NF P 94-068 [20] e result shows that the sludge does not contain any clay fraction because its methylene blue value (MBV) is equal to 0.45.
Figure 1 shows the particle-size distribution curve of the marble sludge carried out by the sedimentation method, according to the standard NF P 94-057 [21].According to this curve, the maximum particle size of marble grains is 63 micron.
In addition, the absolute density and the Blaine specific surface (BSS) of the marble sludge are, respectively, 2.69 g/cm 3 and 9459 cm 2 /g.Finally, the Atterberg limits of the marble sludge were also determined.ey are calculated according to the requirements of ASTM D4318-17 [22].e results of this test are shown in Table 2.
According to the results presented in Table 2, the initial water content and liquidity limit of the marble sludge are, respectively, equal to 30% and 31%.Indeed, the initial water content in the sludge represents its liquidity limit.e undefined plasticity limit indicates that the sludge is free from any fine clay proportion. is result was confirmed by the VBS value which is in the order of 0.45.

Cement.
e cement used was CEM I 42.5, in conformity with the standard NF EN 197-1 [23].e chemical composition of this cement is shown in Table 3. e absolute density and the bulk density of the used cement are, respectively, equal to 3.08 and 1.03 g/cm 3 .In addition, its BSS value is equal to 3100 cm 2 /g.

Aggregates.
e physical characteristics of the aggregates used in the preparation of concrete specimens are shown in Table 4.

Admixture.
e employed admixture was a superplasticizer (SP) used to increase markedly the workability of concrete.e degree of saturation of SP, determined by the Marsh cone test in accordance with the standard NF P18-507 [24], shows that the maximum of the ratio superplasticizer/cement is equal to 1.2%.

Methods.
is study aims to valorize of the sludge waste of the cutting operation of marble cutting.e main purpose of this work is to investigate the direct incorporation of marble sludge in self-compacting concrete.
e experimental study is composed of two main parts: MSG rheological behavior and a new technique for mixing self-compacting concrete with MSG.

Experimental Study of MSG Rheological Behavior.
e most important condition that must satisfy the MSG is its penetrability on the granular matrix of concrete.e two main parameters influenced the penetrability are the granularity of its solid phase and its rheological characteristics (fluidity).
To determine the optimal water content of the MSG that gives the best penetration and the sufficient rheology, we investigate an experimental study of MSG rheological behavior as a function of the added water amount.For this, eight MSGs termed MSG1, MSG2, MSG3, MSG4, MSG5, MSG6, MSG7, and MSG8 were prepared with different water/sludge ratios, respectively, equal to 0.6, 0.8, 1, 1.2, 1.4, 1.6, 1.8, and 2. It should be noted that the marble sludge amount is constant for all grouts.e composition of the MSG is presented in Table 5.
To prepare the different MSGs, we used a propeller mixer with a controlled rotation speed.In order to 2 Advances in Civil Engineering completely disperse the marble sludge grains in the water, to eliminate any possible agglomerate, and to obtain homogeneous MSG, the total mixing time was xed as 7 minutes at a maximum rotation speed of revolution/ min, thus guaranteeing the same mixing energy for all the tested MSGs.Advances in Civil Engineering e detailed mixing procedure is as follows: Step 1. Introduction of marble sludge into the water, 1 min at 400 revolutions/min.Step 2. Grout mixing, 6 min at 700 revolutions/min.We also verified that, at the end of each mixing, no segregation is visible at the bottom of the mixing bowl and that the MSG temperature is always within a limited range of 24 ± 1 °C.
All tests on MSG were made within 90 s after the end of mixing in order to ensure the same MSG state.

Experimental Study of a New Technique for Mixing Self-Compacting Concrete with MSG.
is part of our experimental investigation needs us to select the most appropriate mixing method for grout and concrete, and thus to obtain SCC having good rheological properties, choosing the better mixing method of the SCC with the MSG is essential.For this purpose, we prepare and test four samples of the selfcompacting concretes SCC1, SCC2, SCC3, and SCC4 mixed with MSG having different water/sludge ratios.
e excess paste method was used for formulating the four self-compacting concretes according to the requirements of the standard EN 206-1 [25].
is method considers the concrete as a biphasic material, consisting of a fluid phase (paste) and solid phase (aggregates) [26].e four SCCs are "SCC30" with a flow class of SF2.For this class, the slump value must be between 66 and 75 cm and the minimum required 28-day compressive strength is 30 MPa. e cement dosage was set as 400 kg, and the weight ratio of gravel to sand was set at 1 (G/S � 1).
Table 6 presents the dosage of the four self-compacting concretes.
e four concretes, SCC1, SCC2, SCC3, and SCC4, differ by the mixing methods.e mixing methods are presented in Table 7.
e four concretes were tested, in their fresh state, through the following tests: slump flow test, L-box test, V-funnel test, sieve stability test, and measuring the air content were performed on fresh concrete (Figure 2).

Influence of the Water/Sludge Ratio on the Grain Dispersion of Grout.
In order to evaluate the water content influence on the dispersal potential of the grains in the different prepared MSGs and on its incidence to their rheological behavior, we passed all the mixed grouts through the 63 micron sieve (Figure 3).e dispersion percentage of the different MSGs is presented in Figure 4. We remarked that the increase of the water/sludge ratio makes the passage of grout through sieve very easy.We also remarked that if the water/sludge ratio is equal to 1.2, the MSG is totally passed through the sieve.
We can thus conclude that the more the water/sludge ratio, the more the MSG disperses totally. is is due to the increase of the intergranular distance between MSG grains and the decrease of the volume concentration of the solid.Consequently, the interaction number and the intensity of the friction between grains were reduced during the MSG flow.
is result can be theoretically approved by the following formula, which estimates the intergranular distances "e": e(μm) � 2.10 4 (water/sludge − 0.12) where BSS is the Blaine specific surface of the marble sludge (cm 2 /g).e intergranular distances, of the different MSGs, estimated using Equation ( 1), for BSS � 9450 cm 2 /g, are given in Table 8.According to the given results, we can confirm that the distance between MSG grains increases with the water/sludge ratio.
It is noted that the total dispersion of the grains does not mean a stable grout.However, using a mini-cone test, we observed the segregation phenomenon for the MSG with the water/sludge ratio higher than 1.4.
Finally, the particle-size distribution curves of all MSGs are prepared by the sedimentometric test according to the NFP 94-068 standard [21].
e results showed that the particle-size distribution curves of the grains of MSG with 1.2 water/sludge ratio are the same as that the natural sludge.Indeed, the total dispersion of MSG grains with the water/sludge ratio equal to 1.2 was also confirmed.

Influence of the Water/Sludge Ratio on the Grout
Density.
e density of MSG was determined with the Fann four-scale mud balance.e measurement results of MSG densities are presented in Table 8 and Figure 5.
According to the results presented in Figure 5 and Table 8, we can notice that the experimental density of MSG decreases by increasing the water/sludge ratio. is is due to the increase in the free water amount between the marble grains which is related to both the increase of water content and to the decrease of volume concentration of the solid of MSG.
e last result was confirmed by the theoretical density values of different MSGs given by the following expression: where M s is the sludge mass, M w is the water mass, V s is the sludge volume, and V w is the water volume.
V s and V w can be presented, respectively, by the two following relations: Advances in Civil Engineering

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where ρ s and ρ w are the unit weights, respectively, of sludge and of water.By using Equations ( 2)-( 4), the relationship between theoretical density and water/sludge ratio of MSG can be expressed by the following relation: e results presented in Figure 5 and Table 8 show that the theoretical and the experimental density values present a good agreement.Indeed, the in uence of the water/sludge ratio on the MSG density was con rmed.

In uence of the Water/Sludge Ratio on the Volume Concentration of Solid.
e volume concentration and granularity of the solid phase of grout are two of the most important factors a ecting the rheological characteristics of the grout.
e theoretical expression of the volume concentration of the solid of the grout, denoted (V c ) e , is as follows: By using Equations ( 3), ( 4), and ( 6), the relationship between the theoretical volume concentration of the solid and the water/sludge ratio can be expressed by the following relation: e experimental expression of the volume concentration of the solid of the grout, denoted (V c ) Exp , is as follows: e theoretical and the experimental volume concentrations of the solid of the di erent tested MSGs are presented in Figure 6 and Table 8.According to the results, we  6 Advances in Civil Engineering can conclude that the volume concentration of the solid decreases by increasing the water/sludge ratio. is is due to the increase of the water amount.We also remarked that the theoretical and the experimental solid concentrations by volume values present a good agreement.

Marsh Funnel Viscometer Test.
e Marsh funnel is used to measure the time required to ll a set volume of grout.
e ow through the small tip at the end of the funnel is related to the rheological properties of the uid being measured.Marsh funnel ow time is used as an indicator of the relative consistency of uids.Longer time to ll one quart indicates that the MSG is more viscous.e calibration for Marsh funnel time is 26 seconds per quart for fresh water.
is test was required according to the standard NF P18-507 [24].
Flow time of the di erent MSGs is presented in Figure 7 and Table 9.According to these results, we remarked that the measured ow time increases rapidly with the water content.We also remarked that if the water/sludge ratio is below 0.6, the MSGs no longer ow, they are not deformed under the e ect of its own weight, and its Marsh funnel viscosity tends to move towards in nity.If the water/sludge ratio is equal to 1.4 (corresponding to a low concentration of the solid), the MSG viscosity decreases until stabilization around 26 seconds which is the Marsh viscosity of water, and consequently, the studied MSG has the same rheological behavior as water.
e results presented in Figure 7 and Table 9 also show the in uence of the superplasticizer on the MSG behavior.Measurements show that, for a water/sludge ratio equal to 0.6, the mix has a character of a grout which proves that the superplasticizer can play the role of a uidifant.It is also noted that, for the water/sludge ratio equal to 1.4, the MSGs have a ow time very close to that of water.
Marsh funnel time provides a single data point that cannot be used alone to specify the grout rheology.Using the ow time and the density, we can determine the equivalent viscosity of MSG by the following expression: where μ e is the equivalent viscosity in Pa•s, t is the ow time of out ow of the volume 0.95 L in seconds, and ρ g is the grout density in g/cm 3 .e equivalent viscosity values of MSG, presented in Table 8, show that this equivalent viscosity decreases with the increase in the water/sludge ratio.

E ect of the Mixing Method on the Rheology of SCC in the
Fresh State

Slump Flow Test.
e slump ow test is the simplest and most widely used test method to quantify the workability of SCC [27].e slump ow, measured according to the standard NF EN 12350-8 [28], is a value system for the ability of concrete to deform under its own weight against the friction of the surface with no external restraint present.e principle of this test is shown in Figure 2(a).Table 10 presents the results of the slump ow tests of the four tested SCCs as the function of the mixing method.
According to the results presented in Table 10, we remarked that, for the concrete SCC1, which we incorporate directly the sludge in its natural state (water content equal to 30%), the dispersion of the grain sludge is almost absent.We also remarked that after mixing procedure cycle, marble sludge was divided into several slurries.Indeed, for this concrete, there is no increase in the paste volume, no homogeneity, and no deformability.Finally, we can conclude that the concrete SCC1 is not considered as a selfcompacting concrete.
With the same reasoning, the sludge dispersed in advance in 1/3 of the total quantity of the gassing water did not give the character of a grout (concrete SCC2).In view of the lack of water, the marble grain dispersion is partial and the concrete deformability is low. is is justi ed with the low slump ow value of 40 cm.

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We also remarked that mixing the concrete SCC3 according to the procedure 3 leads to the increase of the concrete deformability and then the slump flow increases to 70 cm.We also noticed that the best deformability has been obtained with this mixing procedure.e 70 cm slump flow value shows that the concrete SCC3 belongs to the class SF2.
is result demonstrates the positive effect of the use of MSG dispersed in advance in which its objective is to improve the SCC deformability.
e increase in deformability is due to the fineness of marble sludge (9450 g/cm 2 ) which is greater than that of cement (3100 g/cm 2 ). is contributes to the improvement of the workability of the concrete and to the increase of the paste volume since the density of the marble sludge is lower than that of cement. is increase of the paste volume and the dispersion of the marble particles in the water tend to remove the particles sand from each other thereby reducing the friction at the granulate interface.In addition, the increase in the paste volume contributes to the improvement of workability, plasticity, and homogeneity of the selfcompacting concrete.
Figure 8 presents the effects of the water/sludge ratio on the paste volume of the different tested self-compacting concretes.
e results also showed that the good quality of the MSG obtained by dispersion of the marble sludge in 2/3 of the total gassing water amount improves the granulometry of the paste which reduces the intergranular friction between the different fine grains.Indeed, both the free water and the deformability of SCC increase.
Regarding the procedure 4, dispersing the sludge in the total amount of the gassing water gives a very fluid and segregated concrete (SCC4 concrete).
is is due to the hyperfluidity of the MSG and to the superplasticizer effects on its viscosity.We also noticed that the superplasticizer did not act completely with the cement and consequently the deformability decreases.is is justified by the low slump flow value of about 50 cm with the segregation of even grains of the MSG.
is affects the stability of SCC and consequently reduces its resistance to segregation.Finally, we can conclude that the concrete SCC4 has no self-compacting character.
Since the two mixing procedures 1 and 2 produce two concretes SCC1 and SCC2 that do not have a selfcompacting character, for the rest of the tests, we are interesting to study only the rheology of SCC3 and SCC4.

Sieve Stability Test.
e sieve stability test was carried out according to the standard NF EN 12350-11 [29].To perform the sieve stability test, a sample of 10 liter of concrete was allowed to rest for 15 min.en 2 liter of it was poured on a 5 mm sieve from a height of 500 mm, and the percentage of the sample passing the sieve was reported (Figure 2(b)).It has been reported that the variability of test results is poor, especially when the segregation is severe.
e results of the sieve stability test are presented in the Table 11.ese results show that the mixing procedure 4 leads to a decrease of the resistance to segregation (for SCC4, the sieve stability is equal to 18%).In the contrary, the mixing procedure 3 gives a very a high resistance to segregation (for SCC3, the sieve stability is equal to 1.4%).

V-Funnel Test.
e V-funnel flow time (Figure 2(c)) was carried out according to the requirements of NF EN 12350-9 [30].Nonuniform flow of concrete from the funnel suggests a lack of segregation resistance.e V-funnel results were related to concrete viscosity, passing ability, and segregation resistance [31].A long flow time can be due to high paste viscosity or high interparticle friction.
According to the results presented in Table 11, the flow times of the two concretes SCC3 and SCC4 are, respectively, 8.45 and 15.25 s.We can conclude that the increase of the MSG fluidity at a water/sludge ratio equal to 1.2 leads to the decrease of the flow time of the selfcompacting concrete.Beyond this threshold and despite that the MSG is hyperfluid, the observed segregation delays the flow time.
Finally, according to the concordance between horizontal and vertical flows, the mixing procedure 3 gives both self-compacting and self-leveling concretes (SCC3).

L-Box Test.
e L-box test is used to investigate the flow rate and passing ability of SCC in confined spaces [32].It measures the reached height of fresh SCC after passing through the specified gaps of steel bars flowing within a defined flow distance (Figure 2(d)).After the concrete comes to rest in the apparatus, the heights of the concrete at the end of the horizontal portion, h2, and in the vertical section, h1, are measured to compute the blocking ratio, h2/h1.e results presented in Table 11 show that the ratio h2/h1 decreases with the increase of the marble sludge From the values obtained, we notice that SCC4 is outside the recommended range (≥0.8):H1/H2 � 0.4, hence a risk of blockage.On the contrary, the concrete obtained by the mixing procedure 3, SCC3, increases the filling rate. is improves the filling and passage capacitance and consequently prevents concrete blockage in the vicinity of the bars.11 show that the two concretes SCC3 and SCC4 have an air content percentage, respectively, equal to 1.5 and 8%.e 1.5% value proves that the concrete SCC3 has maximum compactness without vibration or clamping, and it is very homogeneous.is homogeneity is due to the good distribution of marble grains and the total dispersion of these grains.

Conclusion
e objective of this work was to study the possibility to gassing the SCC by a prepared MSG and to evaluate the impact of the mixing method on the properties of SCC in the fresh state.
e main results of this study are as follows: (1) e marble sludge has su cient characteristics to be incorporated in SCC (2) e variation of water content of MSG shows that the water/sludge ratio of 1.2 gives the MSG having an acceptable viscosity that makes the penetrability of MSG easy in the granular matrix (3) e dispersion of the marble sludge in the water amount less than 2/3 a ects the neness and the real size of the sludge given a partial dispersion of the grains (4) e dispersion of the marble sludge in the water amount greater than 2/3 has the consequence of removing the grains and having an excess amount of free water causes the segregation phenomenon of SCC (5) Gassing by MSG seems to be a promising method to directly value marble sludge and to improve the rheological characteristics of SCC ( 6) e e cient process is the procedure 3 which respects the universal mixing process: 2/3 of the amount of water for wetting aggregates and 1/3 of water added for the cement hydration reaction (7)

Figure 1 :
Figure 1: Particle-size distribution curve of the marble sludge.

Figure 6 :Figure 7 :
Figure 6: Experimental and theoretical volume concentrations of the solid and water/sludge ratio relationship.

Table 1 :
Chemical composition of marble sludge.

Table 4 :
Physical characteristics of aggregates.

Table 2 :
Atterberg limits of the marble sludge.

Table 3 :
Chemical composition of cement.

Table 5 :
Composition of MSG.

Table 7 :
e different mixing methods.

Table 6 :
Composition of 1 m 3 of SCC with marble sludge.

Table 8 :
e physical properties of the di erent MSGs.

Table 9 :
Marsh funnel flow time and equivalent viscosity of different MSGs.
amount. is result is a consequence of the increase in the viscosity of SCC with the large amount of marble sludge.

Table 11 :
e SCCs obtained by the procedure 3 have both self-leveling and self-leveling characters, a character not obtained when we incorporate the marble ller into the cementitious matrix Figure 8: e e ect of the water/sludge ratio on the paste volume of SCC.Properties of the two concretes SCC3 and SCC4 in fresh state.