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Recycled Concrete Based on Retour de Toupie Aggregates (Fresh Concrete Waste)

SERIFOU Mamery Adama*, JOLISSAINT Obre Sery Paul, ASSANDE Aka Alexandre, EMERUWA Edjikémé

Laboratory of Soil Sciences, Water and Geomaterials, Félix Houphouët-Boigny University, Abidjan, Côte d’Ivoire

Abstract: The toupie is a ready concrete delivery truck (BPE). Accidentally or negligently, if the concrete is not delivered on time, he makes and hardens. It enters the range of waste. In this study, fresh concrete is crushed and reused as a substitute for natural aggregates. A 2-variable experience plan (% sand and% gravel) was used to reduce the number of measurements. The replacement proportions used are 0%, 50% and 100%. Several mechanical and physical properties were measured including compressive strength, tensile strength and absorption. These results show a good correlation between the percentage of replacement and the properties of this concrete. Replacing 50% of natural aggregates (sand and gravel) with recycled aggregates results in a reduction of about 24% in the compressive strength of the concrete under test.

Keywords: waste, fresh concrete, recycled aggregates, properties, natural aggregates

Received April 03, 2020; Revised May 05, 2020; Accepted May 12, 2020

Citation: SERIFOU Mamery Adama, JOLISSAINT Obre Sery Paul, ASSANDE Aka Alexandre, EMERUWA Edjikémé, Recycled Concrete Based on Retour de Toupie Aggregates (Fresh Concrete Waste). American Journal of Materials Science and Engineering, 8 (1). 1-5. January 2020. doi:10.12691/ajmse-8-1-1

1. Introduction

The intensive use of aggregates is an environmental concern of great importance. The recycling of various wastes in concrete has been the subject of many studies. Ceramics, tires, glasses, but also waste from the demolition of bricks and concretes are recycled into concrete. In recent years, crushed concrete after demolition of structures has been studied as a substitute for natural aggregates and has already been the subject of several publications [1,2,3]. However, this material requires prior treatment (iron removal, elimination of impurities, etc.) [4]. Another way of recovery is the use of unused fresh concrete. A new approach for the recovery of this product is studied in this article: it consists in using these recycled aggregates in concrete as a substitute for natural aggregates. Very little work has been done on this type of material as substitute aggregates. Recently, [5,6] use an experimental design with two variables, the water-to-cement ratio and the replacement rate (10%, 20% and 30%). These studies consider aggregates as a sand plus gravel. The effect of granulometry or the granular class has not been studied. It has been shown in these works that the compressive strength decreases with the replacement rate and increases with the curing time.

The objective of our study is to valorize the aggregates resulting from the return of the fresh concrete not used for the manufacture of a hydraulic concrete. Physical characterization tests on recycled aggregates (sand and gravel) as substitute aggregates were carried out according to a two-variable experimental design (sand replacement rate and gravel replacement rate) on the basis of a composition. identical. Several variants of combinations of fine and coarse aggregates between natural and recycled have been tested.

The "Dreux-Gorisse" formulation method was used to make seven compositions that were tested with CEM II 32.5 R. These compositions were established to obtain a C25 / 30.

The influence of these recyclates on the properties of fresh and hardened concrete is presented and discussed.

2. Identifications of Constituent Materials

The materials used in this study are:

- rolled sand from the Girondines rivers

- gravel of the same nature as sand

- recycled aggregates of fine fraction (recycled sand) and coarse (recycled gravel) from fresh concrete of toupie

A cement: CEMII / 32.5 R CE NF from Calcia Bussac meeting the French standard NF P 15-317.

The characteristics of the constituents are presented in Table 1 and Table 2.

Table 1. Physical characteristics of aggregates used

Table 2. Chemical composition of cement (average values in%)

3. Methodology

Concretes were produced after the substitution of 50% or 100% of natural sand and gravel with recycled aggregates. The optimal number concrete mixes after substitution is seven mixes of which the factor 1 (F1) is the percentage of recycled sand and the factor 2 (F2) is the percentage of recycled gravel. The experiment plan is shown in Table 3.

The reference concrete is an ordinary 28-day strength concrete of 25 MPa with plastic workability. The composition of the recycled concrete is identical to the reference concrete. However, to ensure the same workability in the case of recycled concrete and because of the high water absorption of recycled sand, a water correction was necessary. Indeed, different authors as [7,8,9] reveal that the water absorption of recycled aggregates is inevitable and may affect the workability of fresh concrete. These require an additional amount of water with plastic workability similar to natural aggregate's concrete. The amount of water added to recycled fine aggregate concrete is 78.39 L to provide adequate workability. This amount of water is higher than that added to recycled gravel concretes (36.16 L). Table 3 summarizes the composition of the seven concretes tested.

Table 3. Experiment Plan

The mechanical strengths of concretes were measured at 1, 14 and 28 days on 16x32 cm² cylindrical specimens for compression, 11x22 cm² for splitting tension and on 7x7x28 cm³ prismatic specimens for flexural tensile. Water absorption was also measured according to the AFNOR recommendations. Table 4 present the composition of the various concretes.

Table 4. Compositions of the various concretes ('R' = recycled, 'N' = not recycled, the first letter concerns the percentage of sand and the second letter that of grave

Figure 1. Evolution of compressive strength during curing (28 days) for reference concrete and recycled aggregate's concrete

4. Results and Discussion

4.1. Compressive Strength

Figure 1 shows the evolution of compressive strength during curing for reference concrete and recycled aggregate's Concrete. A similar behavior is noted for all the concretes. However, recycled aggregate's Concrete have very low resistance at a young age with slower hydration kinetics. This resistance at a young age is similar for all recycled concrete (4 MPa on average) regardless of the percentage of recycled material. There is a difference between these concretes in terms of compressive strength only from 14 days of cure. The Eurocode 2 model has been used to connect the resistance with the cure (Equation 1) in Figure 1. It is shown that this model is also valid for recycled aggregate's Concrete. However, there is a significant difference of the order of 2 MPa (50% in relative) to 1 day of cure.

[picture] | (1)

with s = 0,25 (Cement CEM II 32,5 R).

4.2. Tensile Strength by Splitting and Bending

The relationship between tensile strength and percent replacement is shown in Figure 3. In this figure, measurements of both types of tests (bending and splitting) are presented. There is a slight decrease in tensile stress. For a replacement rate of 25%, the stress is of the same order of magnitude as for the reference concrete. There is also a higher resistance to bending than to splitting for replacement percentages greater than 25%.

Figure 2. Relationship between mechanical strength and total percentage of recycled aggregates

Figure 3. Tensile strength as a function percentage of recycled aggregates (measured by bending and splitting)

Figure 4. Absorption of concretes as a function of time and percentage of replacement at 28 days of maturation

4.3. Absorption

Figure 4 show the variation of the water absorption as a function of time and the percentage of recycled aggregates. Thus, many studies show that water is one of the most sensitive constituents affecting concrete properties. This is confirmed physically by several important roles played by water: hydration of cement grains, plasticity of fresh concrete and internal cohesion of fresh concrete [10,11]. Excess water in the concrete can be accompanied by side effects that are detrimental to the quality of the concrete. What is observed at the BRR, the amount of water used for hydration is in excess and its compressive strength is low. According to [12], recycled concrete aggregates continue to absorb water even after mixing. Thus, the lower quality of our recycled concrete is not only related to the amount of water used. This lower quality can also be attributed to the lower strength of the recycled aggregates and the quality of the interface areas [13,14]. Figure 4 shows the variation of the absorption of the various concretes as a function of the maturation time. In this figure, the influence of grain size and quantity on concrete absorption is significant. The BRR absorbs more than the BNR and BRN, it contains a large amount of recycled aggregates than the others. In addition, Recycled Fine Aggregate Concrete (BRN) absorbs more (256.39L) than Recycled Coarse Aggregate (BNR) concrete (214.16 L). Fine aggregates have a higher specific surface area. Therefore, the finer the recycled granulate, the greater the quantity of water adsorbed on its surface per unit volume. In addition, the nature of fine aggregates (old mortar) accentuates this absorption effect of recycled concrete. Also, it appears that the replacement of 50% recycled gravel without sand replacement has no effect on this physical parameter.

5. Conclusion

The resistance at a young age is similar for all recycled concrete (4 MPa on average) regardless of the percentage of recycled material for the compressive strength.

For a replacement rate of 25%, the tensile strength is of the same order of magnitude as for the reference concrete. There is also a higher resistance to bending than to splitting for replacement percentages greater than 25%.

The absorption of gravel and recycled sand from fresh concrete is high, being respectively 4.3% and 13%. The replacement of 50% recycled gravel without sand replacement has no effect on absorption.

The properties measured on the concretes studied show a possible use of the recycled aggregates of the fresh concretes at percentages lower than 50% of substitution to guarantee acceptable properties in applications of prefabricated elements (paving stones, concrete blocks, etc.).

References

[1]   | Gomez-Soberon J., (2002). “Porosity of recycled concrete with substitution of recycled concrete aggregate: an experimental study”, Cem Concr Res; 32 (8)1301-11.
[2]   | Tu T. Y., Chen Y. Y. and Hwang C. L., (2006). “Properties of HPC with recycled aggregates”, Cement and Concrete Research, 36, 943-950.

[3]  
Kou, Shi Cong, Poon, Chi Sun, and Etxeberria, Miren, (2011). “Influence of recycled aggregates on long term mechanical properties and pore size distribution of concrete”, Cement and Concrete Composites,Bish, D. L. and Howard, S. A., (1988). "Quantitative phase analysis using the Rietveld method." J. Appl. Crystallogr., 21, 86-91.

[4]   | Bodet R., (2003). “Substitution des granulats alluvionnaires dans l’industrie du béton par les granulats marins, concassés ou recyclés”, CERI, ISSN 0249-6224.
[5]   | Correia S., Souza F., Dienstmann G. and Segadaes AM., (2009). “Assessment of the recycling potential of fresh concrete waste using a factorial design of experiments, Waste Management”, 29, pp. 2886-2891.
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[12]   | Hansen T.C. and Narud H., (1983). “Strength of recycled concrete made frorn mrshed concrete comse aggregate”, Concrete International, Vol. 5, No. 1, pp 79-83.
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