Volume 12Enero - Diciembre 2022

The demands for construction materials are increasing, their sources are scarce and the management of construction and demolition waste is very complex. The research that supported this article sought to study the characteristics of coarse aggregate for construction from civil works waste, and compare them with traditional virgin aggregates, in order to assess their possible use. We worked with three sources of raw material for recycling: masonry walls, precast tiles, and cast-in-place concrete (test cylinders); all facilitated by the LanammeUCR.

The standards established by INTECO were followed, both for the characterization of the recycled aggregates and for the mix designs. Three different percentages of recycled coarse aggregate were used in the mixtures, substituting the natural one. The results showed small variations regarding the behavior of the virgin aggregate, especially in absorption, unit weight and wear. Very favorable results were obtained in terms of the compressive strength of the concretes with recycled coarse aggregate, always contemplating a mix design that adjusted to its characteristics. Among the limitations is that the durability of manufactured concrete was not studied; recycled fine aggregate was not used either. Both phenomena will be addressed in future research. At the end of the investigation, it is concluded that the recycling of coarse aggregate is technically feasible.

This research aims to determine the effects of the use of curing products in hydraulic concrete through laboratory conditions. Although research and technical specifications of curing products indicate improvements in concrete curing, their use and possible advantages must be experimentally verified for the conditions and types of concrete manufactured in Costa Rica. Three types of curing products are used, the first corresponds to a transparent silicate-based curing product that does not produce membrane (C1), the second is a resin-based membrane-forming curing product (C2) and the third is a product Colloidal solution based film-forming curing agent (C3). Through laboratory tests, the compressive strength, modulus of rupture and change in length (expansion or contraction) of concrete are determined for different curing conditions. In general, the results indicate that curing products, at any age of application, do not reduce the expansion or contraction of concrete. For curatives to be adequately effective in developing resistance to shrinkage and flexure in concrete, it must be cured with water for a minimum of three days prior to application of the product. The results suggest better results when applying the curing product 7 days after keeping the specimens in the wet room. 

The objective of the research was to carry out a repeatability and reproducibility study in representative samples of small wooden specimens from Spathodea campanulata, Fraxinus americana and Albizia Plurijuga. The experimental strategy assumes two stages. The first consisted of the analysis of the results of the frequencies measured in the three angiosperm species. Its objective was to validate the homogeneity and representativeness of the woods under study. The second stage was oriented to the study of the variations of the frequency results. Its objective was to build repeatability and reproducibility tables and their analysis of variance. A completely randomized and balanced design was prepared. The experimental unit consisted of three homogeneous groups of 40 test tubes of each species. For each species studied, crossover repeatability and reproducibility studies were carried out. The results indicate that for S. campanulata, 97.7% of the total variance is due to the instrument while 2.3% to differences between operators; for F. americana, 99.2% of the total variance is due to the instrument and 0.8% to differences between operators, while for A. plurijuga, 100% of the total variance is due to the instrument while there is no variability due to differences between operators.

In this investigation, the performance and cost of workforce, material, and equipment in the application of plaster with industrialized mortar were estimated. The measurements were made in three housing projects of one and two levels, located within Alajuela, Heredia, San José or Cartago, Costa Rica. In the first two, mortars of different brands were used, however, the application methodology was manual in both cases. In the third project the same mortar was used as one of the previous projects, but it was applied mechanically. For the data analysis obtained, the statistical student-t test was used, with a reliability of 90%. It should be noted that the results are valid only for projects with characteristics like the ones used in this study.

According to the results, the cost of the plastering applied manually is very similar to the one applied with a sprayer machine, since the savings in workforce cost is approximately equivalent to the amount necessary to amortize the equipment and the additional cost of the projectable material.

Due to the scarcity and high transportation costs of stone aggregates in the east and northeast of Bolivia, different alternatives have been sought for their partial or complete replacement in the construction industry and, specifically, to produce concrete. The objective of this research is to evaluate the workability, compressive strength, and ultrasonic pulse velocity (UPV) of concrete produced entirely with coarse lateritic aggregates and a commercial superplasticizer additive. Using the IPT/EPUSP method, concrete with coarse lateritic aggregate was dosed for 30 MPa (design compressive strength). Five different percentages of additive (by weight of cement) were considered: 0% (reference), 0.6, 0.8, 1 and 1.2%. Although the superplasticizer additive improves workability at higher percentages, the mixtures with 0.6, 0.8 and 1% presented higher compressive strength and VPU, when compared to the reference (0%). 1.2% of additive presented the lowest values ​​of compressive strength and VPU. The use of additives, in this case superplasticizer, is beneficial for the workability and compressive strength of lateritic concrete, but the most appropriate content for its use must be defined.