Introduction: This research article “concrete brick with the addition of recycled rubber” was carried out in 2019 at the Faculty of Civil Engineering of the UNSA.

Problem: The need to close the gap in the housing sector, especially for people with low economic resources and contribute to the reduction of atmospheric pollution due to the burning of tires in the manufacture of artisan bricks in the city of Arequipa.

Objective: To find a more economical masonry unit with the same resistance as mechanized bricks, which can be manufactured and used by the inhabitants of the poorest segments of the city, using the rubber from used tires.

Methodology: For the research we induce the object of study, through different additions of rubber in the mixture, this experimentation allows us to find through different tests, the physical and mechanical properties of the LCR, describing the results of the tests carried out on the LCR masonry units and KKH10.

Originality: In the bibliographic review the use of recycled rubber is found in concrete, we propose to find a brick made with a mixture of concrete and recycled tire rubber fibers to replace the fine aggregate that we will call “Bricks with Recycled Rubber” (LCR), our purpose is that it achieves the same characteristics of a type IV unit and meets the minimum requirements established by Standard E.070

Limitations: It has not been had since the materials used are of universal use, although it could be the quality of cement.

Results: The LCR-I brick, which is classified as type IV, is of good quality, handcrafted, and friendly to the environment. This brick has a cost of $ 0.251 US dollars, that is, 12% cheaper than the most widely used mechanized brick in the city.

The recycle of disused rubber and other materials in construction is a necessity and of great help to reduce the environmental impact generated by these materials, as they are produced without any waste mitigation plan.

In today’s world, the advances in research of innovative, ecological, economic and quality materials used in construction are growing, but the problem of waste is being aggravated in developing countries where the awareness about the issue has not yet been realized, that is why the need to resort to greener practices and that the preservation of resources is achieved through the concepts of reduction, reuse and recycling. [12].

Therefore, there is an urgent need to improve existing applications and develop new applications for recycled tires and one of the applications that is being investigated is the use of waste tire rubber as a partial replacement for conventional aggregates in concrete applications [2]. So far, a great deal of research has been done to detect the effects of rubber particles on concrete properties and most forms of recycling consisted of crushing and shredding scrap tires into various particle dimensions and using on concrete mixture.

On the other hand, there are research that focuses on the use of recycled rubber in the production of concrete, most of the studies reported were on normal strength concrete with waste tires as a replacement for natural aggregate, so there are few studies available that analyze the effect of adding recycled rubber to high-strength concrete, therefore further studies are required to evaluate the performance of highstrength concrete containing recycled rubber. The concrete made with rubber fibers makes it lighter and more ecological.

The disadvantages of conventional concrete are the cracking due to contraction and expansion, while in different investigations it was shown that rubber is suitable to improve the previous disadvantages of unit weight and reduction of cracks, which make it possible to use it in places where it is require larger non-structural concrete elements [18].

In Peru there are several retreading plants, including RELINO S.A. located in the city of Arequipa that repairs and rebuilds tires in addition to other retreading centers which is the most widespread form of tire recycling in our country, although the recycling of tires disabled by mechanical or chemical means for their incorporation into new materials of construction or others is not recognized. There is a background of its application and experimentation in different types of pavements without any application in public or private companies, that is why an ecological, sustainable and quality material is proposed.

The present investigation is of a correlational experimental type, so it was carried out in the concrete laboratory of the Faculty of Civil Engineering of the National University of San Agustín de Arequipa, to obtain the brick with recycled rubber (RRB), fibers of recycled tire rubber were added to replace fine aggregate, in order to obtain the optimum quantity according to our proposed combinations and behavior.

A study of the used materials was performed, as well as the study of the different dosages for the elaboration of the RRB bricks and the respective tests to determine and verify the physical and mechanical properties of the brick.

It was used the most commercialized cement in the city of Arequipa, this belongs to the company Yura S.A. with the Yura IP brand, which is the type of cement suitable for mortars according to studies; the physical and mechanical characteristics of Yura IP cement are shown in table 1, below.

The Peruvian technical standards establish a large part of the tests on aggregates, so we have: NTP.400.012.2013: “Granulometric analysis of fine, coarse and global aggregate.”, NTP.400.017.2011: “Method of test to determine the mass per unit volume or density (unit weight) and the voids in the aggregates “, NTP.400.022.2013:” Standard test method for the specific weight and absorption of fine aggregate “; additionally, there are the following international standards ASTM C-33: “Specifications of Aggregates for Concrete”, ASTM C-75: “Sampling of Aggregates’: ASTM C-128:” Standard Test Method for Density, Relative Density (Specific Gravity), and Absorption of Fine Aggregate “and ASTM C-136: ‘’ Granulometric analysis of fine and coarse aggregate”.

For the respective sampling, the aggregates must be clean or free of solid impurities or others that affect their properties before and after mixing, “La Poderosa” quarry was chosen since it showed good results for concrete analysis in other investigations, the sample was prepared according to NTP400.010.2011 “Aggregates: extraction and sample preparation”.

The city’s materials were used, knowing that there are stone aggregates produced in the city that are the most used in investigations due to their ideal characteristics for construction, such as aggregates from the SUPERMIX company, La Poderosa, and Yura IP cement., being the ones used in order to focus on the behavior of the new incorporated material. The recycled tire rubber fibers that are the aggregate to be incorporated in the study are sourced from retreading plant RELINO S.A., which was visited to learn about the process of obtaining and marketing this material.

The materials used in the present investigation were subjected to different tests to obtain their properties.

The specific weight of the sand is shown in Table N°2, which shows an acceptable result in comparison to the recommendation of Porrero S. Ramos R [16], which indicates an optimal value for the fine and coarse aggregate of 2.5 to 2.7 of non-light aggregates, while a test was not carried out for rubber fibers due to the lack of regulations for our experimental material and complex composition.

According to the suggestion by the author Porrero S. Ramos R [16], the usual values of loose unit weight for coarse aggregate is from 1.4 to 1.5 and for fine aggregate is 1.5 to 1. 6, so that the coarse sand having a loose unit weight of 1,506 presents good characteristics, being necessary the determination of this value in the rubber fibers, taking into account that the size of the fibers range between 0.5 to 4 cm, which is necessary for the calculation of quantities for the elaboration of the present investigation. The usual compacted unit weight values f or coarse aggregate are from 1.5 to 1.7 and for fine aggregate they are from 1.6 to 1.9, so the present fine aggregate has good characteristics.

The water used was taken from the drinking water service network of the SEDAPAR company in the city of Arequipa.

For the design of standard concrete (conventional concrete) and for the design of non-conventional concretes (with the addition of rubber fibers), compression tests of cubes of 5 cm on each side with different preliminary dosages are necessary to find the appropriate one. dosage for experimentation. Different tests were carried out with different amounts of cement-aggregate in 15%-85%, 25%-75%, 30%-70% (see Table N ° III), coinciding with the guide studies, it was conceived that the results were encouraging for a good dosage except for the mixture with 15% cement, this being very weak and inadequate for our study, being discarded.

Knowing the optimal properties of our materials for our study, we proceeded with the design of the dosages by means of the experimental methodology, starting from a design basis already explained. By means of the compression test of cubes of 5 cm per side and in different dosages of rubber in the concrete, an optimal dosage was obtained at the age of 7, 14 and 28 days. The optimal design of the present study was obtained by varying the percentages of rubber fibers in replacement of fine aggregate in volume of 10, 15, 20 and 30% and with the constant amounts of cement in 25% and 30% in volume of base proportion P0.

The optimal dosage was chosen according to the analysis of compressive strengths and optimal densities, the best design option being the dosage of 25% cement - P2 with 15% rubber fibers replacing sand, having the strengths of 103,33 Kg/ cm2, 123,69 Kg/cm2 and 155,90 Kg/cm2 at the ages of 7.14 and 28 days respectively and with a density of 1.92 g/cm3. The objective of the research is fulfilled by obtaining an economic material, with quality and ecological, being the dosage by weight of the materials used for the manufacture of a concrete masonry brick with recycled rubber fibers, considering 10% waste and complying with the characteristics of the masonry unit for structural purposes.

Concrete bricks with RRB recycled rubber fibers meet the requirements for alveoli percentages by not exceeding 30% of the percentage of alveoli being considered as solid units, while the calcined clay brick KKH10 are considered as hollow unit when exceeding the established percentage.

Given the results of dimensional variability as shown in Table 7, RRB I brick is type IV, RRB II is type V and calcined clay brick is considered type IV.

Considering the classification of masonry units of the E.070 standard, in the warping test the calcined clay unit KKH10 is classified as type IV, the RRB I unit as type IV and the RRB II unit as type V.

It is known that the units with absorption greater than 22% have higher porosity and low resistance to weathering, the percentages of CSF absorption being very low compared to the calcined clay KKH10 units that reach 16%.

Like absorption, the maximum absorption data results indicate that RRB concrete bricks have low percentages compared to KKH10 calcined clay bricks.

The densities obtained from the RRB were relatively positive compared to ordinary concrete, varying from 2.4 - 2.5, since low-density rubber fibers were included.

The suction test gave the following results for KKH10-47.88, RRBI-12.95 and LCRII-8.49, which shows the disadvantage of setting the calcined clay brick since it will subtract water from the mortar being necessary to use wet units in the laying of walls, such treatment is unnecessary in the laying of the RRB bricks.

The bending tensile test gives better results for the RRB I brick compared to the KKH10 calcined clay brick, due to the rubber fibers inside.

The indirect tensile test shows that the RRB II brick is better than the calcined clay brick KKH10 by 0.6 kg/cm2 as shown in Table 14.

According to the results of the unit compression test, the RRB I unit is classified as type IV, the RRB II unit is classified as type III and the calcined clay unit KKH10 is classified as type IV.

The compression results of masonry prisms indicate that those made with RRB units are better by approximately 14 kg/cm2 and 4 kg/cm2 than those made with KKH10 calcined clay units, according to the standard.

The results of the diagonal compression test of walls corroborate a greater resistance for the RRB walls in approximately 2 kg/cm2 higher than the KKH10 calcined clay walls, meeting the requirements of the standard.

The modulus of elasticity is found for the experimental materials by means of prism compression, being lower, but not far from the value of the norm, which considers an ideal of 700 times f`m:

The shear modulus was found thanks to the diagonal compression tests in the walls of the experimental material, obtaining lower values, but not far from the ideal according to the norm and bibliography that establishes it as 0.4 times E´m:

Given that there are the necessary materials in the city and the proven quality of the experimental brick, then, the necessary quantification of materials will be shown for the elaboration of a concrete brick with rubber fibers from tires:

In the current market, the mechanized calcined clay brick KKH10 has a cost of 0.286 dollars, while the cost of the experimental RRB-I brick has a cost of 0.251 dollars, taking into account that this cost includes unskilled labor, and its yield is 80 units/day, costing 12% less than mechanized brick. It should be taken into account that the production of these RRB bricks will increase since it will be in charge of the population that in order to reduce costs will not skimp on working hours increasing their performance for their own well-being.