The properties of preplaced aggregate concrete technology contain the industrial waste-material and the various shapes and sizes of coarse aggregate

The success of preplaced aggregate concrete technology depends on two main factors which are potential grout and coarse aggregate. This research was conducted experimentally to determine the effect of using two different fly ash sources as an alternative for the partial replacement of cement and several size and shapes of coarse aggregate on the compressive and tensile strength of PAC specimens. This involved the use of seven concrete mixes with a low water-cement ratio of 0.4 and cement to sand ratio of 1:0.75 to produce standard cylinder specimens of concrete containing rounded and crush aggregate. Moreover, fly ash was added at a dosage of 5% and 10% of cement weight while three shapes and sizes of a rounded and crushed aggregate at 20 mm, 30 mm, and a mixture of the two were also applied. The results showed the compressive strength of specimens with different sizes or a mix of rounded aggregate in PAC exhibited a similar performance with 30 mm of crushed coarse aggregate. Furthermore, the specimen with a higher content of calcium fly ash demonstrated a more rapid strength at an early age of seven days than those with lower content. Therefore, the partial replacement of cement with industrial waste material in the form of fly ash in preplaced aggregate concrete has the ability to save up to 10% of cement and also produce certain environmental benefits.

Study on the Suitability of Reclaimed Asphalt Pavement Aggregate (RAPA) in Hot Mix Asphalt Production

The main objective of this study was to evaluate the suitability of recycled asphalt aggregate with fresh aggregate in hot mix asphalt production by using experimental laboratory investigation. Also, Non-probable sampling techniques were adopted to collect a sample. The engineering properties of extracted Reclaimed asphalt pavement aggregate and the fresh crushed aggregate were identified based on standard specification before starting the Marshall Mix design, Then the Marshall Stability test was conducted on crushed aggregate with three different aggregate gradation sizes 5.0%, 5.5% and 6.0% by weight of aggregates and with five different bitumen content 4.0%, 4.5%, 5.0%, 5.5% and 6.0% by weight of total mix. Depending on the selected aggregate gradation Marshall Stability test was conducted for reclaimed asphalt pavement aggregate with a replacement rate of 5.0%, 15%, 25%, 35%, 45%, 55%, and 65% by weight of crushed aggregate to determine its optimum bitumen content according to National Asphalt Pavement Association method (NAPAM). A total of 64 mix designs and 190 specimens were prepared. Hence, Marshall Stability and Moisture Susceptibility test with 3-trials, hence rutting test with 2-trials. From 190 specimens, 45 were for the control mix, 105 were for replacement proportion, 36 were for Moisture Susceptibility and 4 were for Rutting Based on the Marshall Test results and their performance tests such as Moisture Susceptibility and Rutting was performed to maximum allowable replacement percentage was compared with standard specification. The optimum bitumen content result obtained in percent was 5.1, 5.04, 4.98, 4.87, 4.81, 4.74, 4.67 and 4.53 for 0 % (control), 5.0%, 15%, 25%, 35%, 45%, 55% and 65%, respectively. The experimental value of Tensile Strength Ratio, proportional rut depth and mean rut depth on 45% RAPA replacement was 85.42% and 4.48 %, 2.24 mm respectively. Finally, the test result obtained from the marshal stability and the performance testes indicates that up to 45% replacement of aggregate is reclaimed asphalt pavement aggregate in hot mix asphalt production satisfies the standard specification.

Stemming and best practice in the mining industry: A literature review

In 2015, after amendments to the explosives regulations, stemming became a mandatory activity for all South African mining operations. There are, however, circumstances in which it is thought stemming has an adverse impact on the blasting outcome. Some of these circumstances include blasting in hot holes, in reactive ground, or when blasting a pre-split. In order to determine when stemming is necessary, its role in the control of adverse blasting phenomena and impact on explosive performance were reviewed. Stemming was found to play a significant role in the fragmentation process and burden movement. Additionally, stemming significantly influences the control of flyrock, air-blast, and toxic fume generation. The review of the literature indicates some motivation for not using stemming for pre-split, trim, hot hole, and reactive ground blasting, provided the benefits associated with not stemming the holes outweigh the risks of stemming them. Best practice for stemming from the literature indicates a stemming length of 0.7 x burden is best for larger hole diameters, and 20 to 30 x 0 for smaller hole diameters. Crushed aggregate appears to be the most effective stemming material. The South African explosives regulations pertaining to stemming were found to be consistent with those of Australia and the USA.

Influence of Selected Curing Techniques on Compressive Strength of Concrete From Palm Kernel Shell Ash and Ordinary Portland Cement

This paper discusses the findings of an experimental study on the effect of various curing procedures on the compressive strength of concrete produced by partially substituting portland cement with Palm Kernel Shell Ash (PKSA). Palm kernel shell ash was utilized in a 1:2:4 mix ratio as a partial substitute for ordinary Portland cement (OPC) at percentage levels of 0%, 10%, and 15%. River sand with particles passing a 4.75 mm BS sieve was used, as well as crushed aggregate with a maximum size of 20 mm, and palm kernel shell ash with particles passing a 212 μm sieve. The compressive strength of the test cubes (150 mm x 150 mm x 150 mm) was determined after 7, 28, and 56 days of curing. The results demonstrated that test cubes containing Palm kernel shell ash developed strength over a longer curing period than ordinary Portland cement concrete samples and that the strength changes depending on the amount of PKSA in the cube samples. The findings showed that at 28 days, test cubes with 5%, 10%, and 15% PKSA content in all curing procedures utilized obtained a greater compressive strength. Curing by immersion produced the highest compressive strength in all replacement level while the concrete cured by sprinkling and spraying gives a lower strength in all replacement leve

Assessing the Influence of Aggregates and Cement Types on Fresh Roller Compacted Concrete Mixture

Roller compacted concrete mixture RCC is considered as a sustainable pavement construction material, it is a heavy-duty concrete mixture with zero slump. An attempt has been made in the present investigation to design the fresh RCC mixture using two types of coarse aggregates (crushed and rounded), two types of fine aggregates (silica and river sand) and two types of cement (ordinary Portland and sulphate resistance). Concrete mixtures with dense gradation were prepared and compacted according to modified proctor design procedure. A moisture-density test was used to determine the maximum density and optimum moisture content and of RCC mixtures for each mix. Five different percentages of cement (10-18) % are implemented and six different percentages of moisture (4 – 8) %) % are used to determine the dry density-moisture content relationships. It was observed that the maximum dry density of rounded aggregates mixture is higher than that of crushed aggregate mixture by (4.2, 8.3, 4.2, 4.2, and 5.1) % and (4.1, 1.4, 4.1, 2.0, and 2.7) % for (18, 16, 14, 12, and 10) % cement content respectively for mixtures constructed with silica and river sands respectively with ordinary Portland cement. However, the maximum dry density of rounded aggregate mixture is higher than that of crushed aggregate mixture by (3.5, 4, 7.1, 5.5, and 4.4) % and (2.7, 4.8, 2.3, 4.4, and 4.2) % for (18, 16, 14, 12, and 10) % cement content respectively for mixtures constructed with silica and river sands respectively with sulphate resistance cement. It was concluded that 12 % of Portland cement and (6 to 7) % of moisture are proper combination when silica or river sand were implemented, while (12 and 14) % of sulphate resistance cement and (6 to 7) % of moisture are proper combination when silica or river sand were implemented. abstract must be a precise and reflection of what is in your article.

Strength and Microstructural Study of Lightweight Aggregate Concrete (LWAC) Using Lightweight Expended Clay Aggregates (LECA)

Concrete is a composite material that consists of a cement and aggregate particles. Microstructure is the small scale structure of a material, defined as the structure of a prepared surface of material as revealed by a microscope. There is strong evidence that aggregate type is a factor in the strength of concrete. The objective of this research is to investigate the properties of concrete that are containing the lightweight expanded clay aggregates (LECA). Digital microscope was used to analyses the formation mechanism of microstructure in concrete. LECA were used in production of lightweight aggregate concrete (LWAC) with the size 50 mm x 50 mm x 50 mm. This paper deals with observation of the concrete microstructure to point out some differences that would be responsible for strength of concrete. The results show that, LECA has several improvements when compared with conventional crushed aggregate. The concrete specimens were used to validate the existence of an interfacial transition zone (ITZ) in concrete. The microstructure features are discussed with respect to their influence on the strength development of concrete.

Influence of Washing of Crushed Aggregate on Mechanical Properties of High-Performance Concrete Containing Supplementary Cementitious Materials

The paper compares macromechanical and micromechanical properties of high-performance concrete containing supplementary cementitious materials and basalt aggregate. The aggregate was either a common unprocessed crushed basalt aggregate or crushed basalt aggregate the coarse fractions (4/8 and 8/16 mm) of which were washed by water and dried before use. The observed macro-mechanical properties were compressive strength, tensile strength, elastic modulus and depth of penetration of water under pressure; the paper is focused on the first observed property, which is the basic material characteristic. On the microscale, the thickness of the interfacial transition zone (ITZ) was determined by nanoindentation. The positive influence of supplementary cementitious materials and aggregate washing on compressive strength was confirmed and the correlation between macromechanical and micromechanical characteristics was proved.