Bond to Bar Reinforcement of PET-Modified Concrete Containing Natural or Recycled Coarse Aggregates

The use of post-consumer plastics in concrete production is an ideal alternative to dispose of such wastes while reducing the environmental impacts in terms of pollution and consumption of natural resources and energy. This paper investigates different approaches (i.e., reducing water-to-cement ratio and incorporating steel fibers or polymeric latexes) that compensate for the detrimental effect of waste plastics on the drop in concrete mechanical properties including the bond to embedded steel bars. The polyethylene terephthalate (PET) wastes used in this study were derived from plastic bottles that were shredded into small pieces and added during concrete batching at 1.5% to 4.5%, by total volume. Test results showed that the concrete properties are degraded with PET additions, given their lightweight nature and poor characteristic strength compared to aggregate particles. The threshold PET volumetric rates are 4.5% and 3% for concrete made using natural or recycled aggregates, respectively. The reduction of w/c from 0.55 to 0.46 proved efficient to refine the matrix porosity and reinstate the concrete performance. The incorporation of 0.8% steel fibers (by volume) or 15% polymers (by mixing water) were appropriate to enhance the bridging phenomena and reduce the propagation of cracks during the pullout loading of steel bars.

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.

The Effect of Using Plastic Strips and Sheets on the Properties of Slurry Infiltrated Fiber Concrete

Slurry Infiltrated Fiber Concrete (SIFCON) is a high-strong material that is regarded as a unique type of high fiber content concrete. This paper aims to study the influence of the use of plastic strips and plastic sheets in the SIFCON slurry. Three sets (normal SIFCON as control, SIFCON with plastic strips, and SIFCON with plastic sheet), in a 1:1.08 cement-sand ratio by weight has been used with water to cement ratio (w/c) by weight equal to 0.3, and superplasticizer equal to 1% by weight. In addition, 6% by volume crimped steel fibers with an aspect ratio of 60 were applied and 1.34% by volume plastic was used, in strips of 5×1cm for both prism and cube samples and in sheets of 25×5cm and 7×7cm for prism and cube samples respectively. The compressive and flexural strength tests studies were conducted on typical cubes of 10×10×10cm and prisms of 40×7×7cm respectively to find out the way the plastic affects the SIFCON properties. The results indicate that the models with plastic sheets placed in SIFCON slurry give the highest compressive and flexural strength whereas the models with plastic strips gave the lowest. The difference percentages in compressive and flexural strength were -27.3, 8, -3.8 and 66.6% for all sets respectively when compared to the control set (using no plastic).

Laboratory Study on the Effect of Water-Cement Ratio on Strength Characteristics of Jet Grouting Columns

Jet grouting is one of the most widely applied soil improvement techniques. It is suitable for most geotechnical problems, including improving bearing capacity, decreasing settlement, forming seals, and stabilizing slopes. One of the difficulties faced by designers is determining the strength and geometry of elements created using this method. Jet grouted soil-cement columns in soil are a complicated issue because they are dependent on a number of parameters such as soil type, grout and water flow rate, rotation and lifting speed of monitor, nozzle jetting force, and water to cement ratio of slurry. This paper discusses the effect of the water-cement ratio on the physical and mechanical characteristics of soilcrete. In the laboratory, sandy soil mixed with cement grout with water-cement ratio varies from (0.7:1 to 1.4:1). To evaluate the characteristics of soilcrete, 96 specimens were prepared in the laboratory and tested at different curing times. The results indicate that the Uniaxial Compressive Strength (UCS) of soilcrete decreases with increasing the (W/C) ratio of the grout, where the soilcrete strength of W/C ratio of 0.7 is higher about 237% of W/C ratio of 1.4 at 28-day; the evolution of the (UCS) is proportional to the logarithm of the curing time; the ratio between the modulus of elasticity (Etg50) to the maximum UCS varies from 113 to 175; when the water-cement ratio increases, the dry density of soilcrete decreases, as a result, the (USC) of soilcrete decreases.

Soft Computing and Multi-Scal Model Technics to Predict the Early Age Compression Strength of Cement Paste as a Function of Polymer Contents, Water-to-Cement-Ratio, and Curing Ages

In this study, the effect of two water reducer polymers with smooth and rough surfaces on the compression strength of Ordinary Portland cement (OPC) was investigated. Three different initial ratios between water and cement (w/c) 0.5, 0.6, and 1 were used in this study. The amount of polymer contents varied from 0 to 0.06 % (%wt) for the cement paste with initial w/c of 0.5 and the polymer contents ranged between 0 to 0.16% (%wt) for the cement paste with initial w/c of 0.6 and 1 were investigated. SEM test was conducted to identify the impact of polymers on the behavior of cement paste. The compression strength of OPC cement was increased significantly with increasing the polymer contents. Because of a fiber net (netting) around cement paste particle was developed when the polymers were added to the cement paste which leads to decrease the void between the particles, binding the cement particles, therefore, increased the viscosity and compression strength of the cement rapidly. In this analysis, the hardness of cement paste with polymer contents has been evaluated and modeled using four different model technics. More environmentally sustainable construction, and lower cost than conventional building materials and early age strengths of the cement. To overcome the mentioned matter, this study aims to establish systematic multiscale models to predict the compression strength of cement paste containing polymers and to be used by the construction industry with no theoretical restrictions. For that purpose, a wide data a total of 280 tested cement paste modified with polymers, has been conducted, analyzed, and modeled. Linear, Nonlinear regression, M5P-tree, and Artificial Neural Network (ANN) technical approaches were used for the qualifications. In the modeling process, the most relevant parameters affecting the strength of cement paste, i.e. polymer incorporation ratio (0-0.16% of cement's mass), water-to-cement ratio (0.5-1), and curing ages (1 to 28 days). According to the correlation coefficient (R), mean absolute error and the root means a square error, the compression strength of cement paste can be well predicted in terms of w/c, polymer content, and curing time using four various simulation techniques. Among the used approaches and based on the training data set, the model made based on the Non-linear regression, ANN, and M5P-tree models seem to be the most reliable models. The sensitivity investigation concludes that the polymer content is the most dominating parameter for the prediction of the compression strength of cement paste with this data set.

Technological Capabilities of Well Cementing

Cementing of casing string is a final operation before the next stage of well construction; it provides maximum operational life of the well. Cementing of casing string is carried out with the use of technology, based on squeezing of the whole volume of drilling mud by special grouting composition. The main purposes of cementing include isolation of water-bearing horizon, strengthening of borehole walls in unconsolidated and unstable rocks. Well cementing process is divided into five subsequent operations. Firstly, grouting mixture is prepared in concrete mixers (cementing units) with necessary water-to-cement ratio and additives. Secondly, prepared grouting solution is injected in a well. Thirdly, the solution is squeezed into the space between the casing pipes and wellbore walls. Then it is necessary to wait until the cement sheath is hardened. And at last, quality control is carried out. For convenient transportation, the equipment for well cementing is installed on the truck chassis (KAMAZ, URAL and etc.). All components are poured in concrete mixer, then the water is added and everything is being mixed until formation of uniform mass, which is later pumped in a well. Oil and Gas Industry Safety Regulations say that «calculated endurance of casing string cementing should not exceed 75% of time of cement thickening, established by laboratory tests». Therefore, it is necessary to carry out all operations of injection of fluids into the well as soon as possible without any incompliances of the cementing technology. With cementing material used and its water-to-cement ratio of 0.5, the average time of cement thickening is 120 minutes, according to laboratory tests. Therefore, a set of operations of injection of fluids should not exceed 90 minutes.