Durability of Bamboo Bio-Concretes Exposed to Natural Aging

In recent years, several studies on the durability of cementitious materials combined with vegetable fibers have been developed. In order to understand the properties of these materials in different environmental conditions, they can be subjected to accelerated aging through several cycles of controlled variations of humidity-temperature, wetting-drying, freezing-thawing. However, analyzes that expose such materials to real conditions of use during their useful life are scarce. As a result, this study analyzed the physical, thermal and mechanical behavior of bamboo bio-concretes produced with different volumes of bio-aggregates, which were exposed to the natural aging of the summer in the city of Rio de Janeiro (Brazil). The cementitious binder was is composed, by mass, of cement (30%), metakaolin (30%) and fly ash (40%). The water-to-cement ratio was as 0.30. The mixtures were produced with bamboo volumetric fraction of 30%; 40% and 50%. After 3 months of natural aging during the Brazilian summer (from December to March), the property determined in the hardened state was the compressive strength. In addition, a visual analysis by photograph was also realize. The results revealed that higher the volumetric fraction, higher the decrease of compressive strength. The visual analysis showed several changes of the external aspect of the bio-concretes.

Eco-efficient concrete, optimized by Alfred’s particle packing model, with partial replacement of Portland cement by stone powder

The partial replacement of clinker by complementary cementitious materials can significantly contribute to the reduction of carbon emissions in the production of concrete. Another alternative to reduce these emissions is to increase the efficiency of the concrete, achieving higher compressive strength with lower consumption of cement. Particle packing models are efficient tools to optimize the composition of the matrix and contribute to the production of more eco-efficient concretes. In this context, the objective of the present study is evaluating the production of concretes with partial replacement of cement by stone powder, optimized by Alfred’s particle packing model, seeking to reduce cement consumption and CO2 emissions per MPa of compressive strength. The replacement content of cement by stone powder was 20% by mass (equivalent to 22.4% by volume). Concretes were produced with different distribution factor (q) - 0.37; 0.21; 0.45 - to verify the influence of fines on the flow between particles and on the efficiency of the produced concrete. The analyses were carried out in terms of properties in the fresh state, hardened state, and sustainability parameters (cement consumptions and CO2 emissions). The application of the proposed method resulted in a higher compressive strength than the expected for the water/cement ratio used (0.5). The most efficient concrete reached the compressive strength of 68 MPa with 240 kg/m3 of cement, which represents 3.5 kg of cement/m3/MPa and 3.1 kg of CO2/m3/MPa, a value below the references found in the literature for conventional concretes. Therefore, the proposed method allows to produce more eco-efficient concrete, contributing to the use of waste and reducing CO2 emissions.

Use of recycled aggregates from civil construction in self-compacting mortar

abstract: The utilization of wastes from demolition in civil construction in self compacting concrete (SCM) has the potential to reduce both the environmental impact and financial cost. In this context, this article aims to verify the behavior of the incorporation of recycled aggregates of civil construction in the mix designs of self-compacting mortar (SCM) in replacing cement, presenting as an interesting alternative to natural raw materials. This study used the EMMA® software to optimize the choice of percentages of fine recycled aggregates when replacing cement. The proportions chosen were 0%, 5%, 15%, and 25%, through the analysis of the granular packing curve of the respective mix designs. The proportion of 0% has in its composition cement, metakaolin, sand, superplasticizer (SP) and water. The parameters obtained, through tests in the fresh state of the mini-slump and mini-funnel V, certified the samples as SCM. The compressive strength and flexural tensile strength tests in the hardened state demonstrated a reduction in mechanical properties of the material with cement replacement. It is concluded that the waste used brick and ceramic can be added in replacement to the cement in SCM without significant loss of properties in the fresh and hardened state.

Recycled PET Sand for Cementitious Mortar

Cementitious materials cause a great impact on the environment due to the calcination of clinker and the extraction of non-renewable mineral resources. In this work, the replacement of quartz sand from the river by PET sand was evaluated at levels of 10%, 20%, and 30%. Tests were performed in the fresh state through consistency, air retention, density, and incorporated air and in the hardened state for compressive strength, flexural strength, density, capillarity, and water absorption. The results show that PET sand is viable in contents of up to 10%, improving the mechanical properties of the mortar and without compromising its workability and incorporated air properties. Above that level, the loss of properties is very excessive, mainly of workability and incorporated air. The incorporated air of the 30% composition, for example, reaches 24%, an excessive value that impacts the properties of the hardened state, making it impossible to use the material at levels greater than 20%. It is concluded that the use of recycled PET sand is a possibility that contributes to sustainable development, as it reduces the extraction of quartz sand from the river, a non-renewable mineral resource.

Comparison between the British and American Methods in Designing Concrete using Local Aggregate in the City of Mosul Preparation

This research included an applied study for the design of concrete mixtures by following the method of the American Concrete Institute (ACl) and the method of the Building Research Center in England (British method) to restriction which of these two methods is more suitable for use and application in the design of concrete mixtures when using local aggregate (gravel and sand taken from the area Badush and Aski Mosul), where job mixes were made using the mixing ratios obtained from these two methods, and a comparative study was made for the properties concrete resulting in the soft state (workability )and the hardened state (compressive resistance), and the results proved the following: A- In general, when discussing the results according to mixing ratios and workability levels, the method of the Building Research Center in England (the British method) gave higher results than the results obtained by the American Concrete Institute method (the American method) when using the above local aggregate whereas results shown increase in (workability) and Compressive strength. This increase amounts to the percentages shown in the table below: Compressive strength (%) Slump test (%) workability 10.48 14.40 Precipitation = 10-8 cm 12.10 21.40 Precipitation = 18-15 cm Table (1-1) B- It is possible to make another comparison, when fixing the proportion of water/cement, it turns out that the method of the Building Research Center in England (the British method) gives higher workability than the method of the American Concrete Institute (the American method) and for the same proportion of cement/ water, the American method gives Higher compressive strength than the British method. C- The building research center method is a more practical and applicable method more than the American Concrete Institute method because it takes the type of cement, the type of aggregate and other properties of the aggregate (especially particle shape) into consideration

ESTUDO DE VIABILIDADE TÉCNICA DA APLICAÇÃO DA ESCÓRIA GRANULADA DE ALTO-FORNO EM SUBSTITUIÇÃO AO AGREGADO MIÚDO NA COMPOSIÇÃO DO CONCRETO

The macro sector of the civil construction industry is a major consumer of natural resources and it generates impacts, identified as social, environmental or economic, and it is necessary to develop studies that aim to rationalize this raw materials consumption and reduce the impacts generated. Since some resources used in the sector are finite, this work’s main objective is to make the concrete more ecological by replacing part of the fine aggregate of its composition for granulated slag from the blast furnace, reducing the need for sand extraction. For this study, tests were carried out with the co-product and with the fine aggregate, evaluating the properties of the concrete in the fresh and hardened states in three mixture types, the first being a reference, the second with 30% replacement and the third with 60% replacement of fine aggregate with slag. Based on the results obtained, it is noted that the granulated blast furnace slag has more similar characteristics to the sand’s; in the fresh state, the concrete showed a similar result in the three mix types; in the hardened state, it was observed that the performance of the concrete in axial compression was satisfactory; while in flexion traction the two proposed mixtures with substitution presented an unsatisfactory result.

Cutting Force When Machining Hardened Steels

This article deals primarily with the problem of determining the cutting force when machining hardened steels. Secondary issues are focused on the evaluation of surface quality on machined samples and the recommendation of cutting conditions. A wide variety of components are used in engineering, the final heat treatment of which is hardening. These components are usually critical in a particular product. The quality of these components determines the correct functioning of the entire technical equipment and ultimately its service life. In our case, these are the core parts of thrust bearings, specifically the rolling elements. The subject of the experiment is machining these components in the hardened state with cubic boron nitride tools and continuous measurement of the cutting force using a dynamometer. The following evaluation assesses the surface quality by both touch and non-touch methods. A structural equation with appropriate constant and exponents was then constructed from the data obtained using the dynamometer.

Mechanical Properties of concrete by reused coarse aggregate with substitution of different percentages instead of natural aggregate and incorporation of Glass fiber

Waste recycling is an option to mitigate the environmental impact resulting from the significant amount of debris generated by the productive activities of the construction. Thus, the aim of the research work to evaluate the use of Recycled Coarse aggregates (RCA) instead of natural coarse aggregate (NCA) in concrete ingredients with 30 MPa compressive strength. The experimental program began with the physical and particle size characterization of the Recycled Coarse aggregates (RCA), and subsequent comparison with the properties of the natural coarse aggregate (NCA). Based on the knowledge of these properties, the production stage began of concretes. Different procedures and literature have been studied in order to achieve the strength of concrete up to 30Mpa by incorporated glass fiber (2 % by addition of cement). It was also the influence of the use of different contents (0, 10%, 20%, 50%, and 100%) of Substitution of natural coarse aggregate by the recycled coarse concrete aggregate in the properties of the fresh and hardened state of concrete. Regarding the strength, parameters increased gradually proportional to the amount of RCA in the concrete from 10 to 20% and decrease strength to the amount of RCA in the concrete from 50 to 100% Substitution of natural coarse aggregate (NCA) in concrete