OPTIMIZATION AND PROGNOSTIC MODEL FOR SPLITTING TENSILE STRENGTH OF CONCRETE PRODUCED FROM GRANITE AND RECYCLED CONCRETE AGGREGATE

 Using recycled concrete aggregates from structural demolition wastes is presenting a potential application in the building industry as a substitute for natural aggregates. It preserves natural resources and brings about a reduction in the space needed as landfill disposal sites. This research was aimed at developing a prognostic model for splitting tensile strength of concrete produced from granite and recycled concrete aggregate. Thirteen rounds of experiments were considered utilizing the Central Composite Response Surface method. Granite was replaced with Recycled Concrete Aggregate (RCA) in varying proportions from 0% to 100% while the water-cement ratio (w/c) was varied from 0.3 to 0.7. Samples were subjected to test after 7, 14 and 28 days curing. It was observed that with a surge in the fraction of RCA, the splitting tensile strength reduced at all levels of w/c ratio. 30% RCA at 0.5 w/c gave the optimum combination that resulted in the highest splitting tensile strength of 2.11  at 28 days. This result is 7.9 % lesser than the control splitting tensile strength of 2.2

Relationship Between Compressive Strength and Splitting Tensile Strength of Palm Kernel Shell Concrete

The use of palm kernel shell (PKS) has gained acceptance in the production of concrete. Compressive strength is the mostly used strength characteristics of concrete. The compressive strength CS of concrete should provide a good basis for predicting the splitting tensile strength STS. The aim of this study is to establish a mathematical relationship between the CS and STS of concrete produced with PKS. In this study, coarse aggregates was fully replaced with PKS at varying water-cement ratios (w/c) for concrete mix ratios 1:1½:3 and 1:2:4. Unit weigth of the PKS, slump, compressive and splitting tesnsile strength were determined. A relationship between CS and STS was developed for the different w/c ratios using exponential function aproximation. Physical property tests carried out on the PKS characterized it as lightweight aggregate with saturated surface dry unit weight of 1.27. The slump revealed that PKS concrete at 0.3 and 0.4 w/c is stiff and not workable. CS and STS at 28day for mix ratio of 1:1½:3 at w/c of 0.3, 0.4, 0.5 and 0.6 were respectively 3.2 and 1.2; 9.4 and 2.1; 10.8 and 2.6; 9.0 and 2.4 N/mm2. The corresponding values obtained for mix ratio 1:2:4 were 3.0 and 1.0, 1.7 and 1.3, 4.5 and 1.6, 7.7 and 1.9N/mm2, respectively. Equations relating CS and STS at 0.3, 0.4, 0.5 and 0.6 w/c were established. It was concluded that PKS concrete produced with mix ratios 1:1½:3 and 1:2:4 performed better in compression and splitting tensile strength at w/c of 0.5 and 0.6

Effect of Epoxy-based Adhesives and Embedded Length in the Bond Strength of Post-installed Reinforcement in Concrete

In Nigerian building industry, there has been events in practice that required improving the structural integrity of existing structures: such as strengthening the interconnection between members. In cases where new structural members are to be added to the existing ones, instead of condemning the whole structure for demolition and rebuilding, post-installation process offers a remedial approach. However, the bond strength (BS) between the reinforcements and the concrete in the post-installed structural element goes a long way to determine the anchorage and effectiveness of the whole structural system. In this study, the BS characteristics of post-installed reinforcement in concrete using four different locally available epoxy-based adhesives in Nigeria were examined. Compressive strength test on concrete cubes and pull-out test on post-installed concrete were carried out for embedment lengths of multiples of 10 and 15 of bar diameters used. Average compressive strength at 28 days was 23.91N/mm2 while the highest BS for 10d and 15d are respectively 5.52 and 6.80 N/mm2 for 12mm bar diameter while corresponding values are respectively 5.38 and 6.35 N/mm2 for 16mm bar diameter. From the results, it was observed that the pull-out force which is a measure of bond Stress is more influenced by the embedded length while increasing the embedment depth from 10d to 15d for the same bar size has less influence compared to increasing bar diameter. The epoxy-based adhesives possess appreciable BS characteristics for post-installed reinforcement in concrete. However, of the three types of adhesives used, Hilti gave the highest BS capacity

Strength and Durability Assessment of Low Water Absorption Glasscrete Blocks for Zero-Spalling Effect in Buildings

Glass waste produced around the world is disposed of carefreely, creating huge piles in landfills and increasing environmental pollution because it is non-biodegradable. This study was conducted to assess the strength and durability of waste glass as a partial replacement for a mortal mix of sharp sand and stone dust. The glasscrete block samples were produced in a 6” metal block mould with 0%, 25% and 50% partial replacement of stone dust and sharp sand respectively. The compressive strength and water absorption tests were conducted after the samples were cured for 7, 28 and 56 days in a laboratory. The highest compressive strengths of 102.333kN and 100.667kN were observed in 50% waste glass partial replacement with sharp sand and 50% waste glass combination with 25% sharp sand and 25% stone dust respectively. The least compressive strength was seen in the control samples of sand and stone dust with no replacement of waste glass. This shows that the addition of waste glass increased the compressive strength of the block samples. The least rate of water absorption was recorded in 50% waste glass, 25% sharp sand and 25% stone dust. It should be noted that the replacement of the waste glass with stone dust performed poorly unlike that of sharp sand. Therefore, it is recommended that 50% waste glass, 25% sharp sand and 25% stone dust should be adopted for the production of glasscrete blocks for a zero-spalling effect in buildings with varying mix ratios. Glasscrete blocks can therefore be used in the waterlogged environment and areas prone to the spalling condition

Investigating the optimal combination for gravel and granite in blended palm oil fuel ash concrete

Global production of palm oil in 2022 was estimated at 73 million metric tonnes. The processing of palm oil generates a huge quantity of waste which is often left unprocessed leading to environmental pollution. Gravels are obtained from weathered rocks and are readily available and cheaper than granite as coarse aggregate in concrete. An innovative way of transforming waste into wealth is by incorporating these materials into concrete for construction purposes. Thus, this study was done to obtain an ideal combination of gravel and granite in palm oil fuel ash (POFA)-blended concrete. A water/cement (w/c) ratio of 0.5 in a nominal concrete mix ratio of 1:2:4 was adopted to achieve a strength of 20 N/mm2. The central composite method of optimization was utilized in designing the experiments. The best combination was determined to be 67% gravel, 33% granite and 32% POFA. This combination produced concrete with compressive strength of 23.80 N/mm2 which is 19% higher than the 20 N/mm2 target strength

Effect of Curing Methods on the Compressive Strengths of Palm Kernel Shell Concrete

Appropriate curing of concrete is necessary to obtain maximum durability and achieve designed strength for concrete exposed to different environmental conditions. Curing is regarded as the means of regulating the degree and extent of loss of moisture from concrete when the cement in the concrete is undergoing hydration. This study made a comparative study of the consequence of adopting different methods of curing on the compressive strength of concrete modified with Palm Kernel Shell (PKS) aggregate. Concrete cube specimens of mix ratio 1:1:2 were cast with water-cement ratio of 0.55. The specimens were cured using four (4) different procedures: immersion, sprinkling, wet-curing and open-air. The concrete samples were tested for their compressive strengths at ages 7, 14, 21 and 28 days of curing. The results obtained show that immersion method of curing has the highest compressive strength at 28 days with a value of 17.07 N/mm2. This was followed by the sprinkling method of curing with 15.78 N/mm2. Wet-curing method has a compressive strength of 14.48 N/mm2 and open-air curing has compressive strength of 13.11 N/mm2. It was concluded that immersion and sprinkling methods are suitable methods for curing PKS concrete

Strength Properties of Steel and Bamboo Reinforced Concrete Containing Quarry Dust, Rice Husk Ash and Guinea Corn Husk Ash

The rising cost of concrete production due to the global recession in world economy caused by the COVID-19 pandemic and the greenhouse gases emitted in the production of cement has necessitated the need for alternative materials for cement. In this study, bamboo strips and steel rebars were used as reinforcements in a ternary blended concrete to determine their strength properties. In alignment with standard requirements for testing, concrete specimens were tested at curing ages of 7, 14 and 28 days for compressive, splitting tensile and flexural strengths. The morphological and bond characteristics of the bamboo were determined through the Scanning Electron Microscopy (SEM) and Fourier Transform Infra-Red Spectroscopy (FTIR), respectively; while its tensile strength was determined and compared with that of steel reinforcement. These results showed that bamboo is ductile and has stretching vibrational spectrum. The combinations of quarry dust, river sand, Rice Husk Ash (RHA) and Guinea Corn Husk Ash (GCHA) yielded compressive and split tensile strengths of 20.4 N/mm2 and 2.18 N/mm2, respectively. Concrete with 50 % river sand and 50 % quarry dust performed better in flexure for both Bamboo Reinforced Concrete (BRC) and Steel Reinforced Concrete (SRC) at 28 days with strengths of 12.75 N/mm2 and 22.49 N/mm2, respectively. Therefore, bamboo, quarry dust, rice husk and guinea corn husk ash can be used for reinforced concrete production

Mix ratio design assessment of interlocking paving stone using both destructive and non-destructive methods

Interlocking paving stones have been produced in most developing countries with no specific method for testing the strength before use. This study presented the mix ratio design assessment of interlocking paving stone strength properties using both destructive and non-destructive methods. Six mix ratios were used to produce the interlocks and tests such as skid resistance, flexural strength, compressive strength and rebound hammer were conducted on 7, 14, 28, 56 and 90 days. All the skid resistance tests had British Pendulum Number (BPN) values greater than 75 specified in Table NA.2 of BS 1338:2003, the interlocking paving stone potential for skid is extremely low. The flexural strength was conducted following IS 15658:2006 and the result ranges from 1.34 – 5.38 N/mm2. The compressive strength result for the mix ratios ranges from 6.20 – 21.78 N/mm2 and mix ratio 1:3 had the highest compressive strength of 19.34, 21.78 N/mm2 at 56 and 90 days respectively. Table 1 of IS 15658:2006 is used to classify the paving stone for use in non-traffic areas based on the compressive strength results. A correlation model was developed combining all the mix ratio average rebound values and compressive strength, the regression equation was produced and an accuracy test was performed to check the regression formula estimates. This study validates the use of a rebound hammer as a non-destructive method on interlocks to predict the compressive strength with 79 % accuracy. Mix ratio 1:3, 1:2 is recommended for use in producing interlocks based on higher compressive and flexural strength

Mechanical properties and microstructure of High-Performance Concrete with bamboo leaf ash as additive

The demand for High-Performance Concrete (HPC) is on the increase for its good workability, high strength, and better durability. HPC are obtained by incorporating supplementary Cementitious Materials (SCM) into concrete to attain a long-term strength and durability performance. Though, several SCM have been investigated in HPC, the use of Bamboo Leave Ash (BLA) in HPC as an SCM has not been considered. Thus, this research investigated the use of BLA as SCM in HPC. The bamboo leaves were calcined in an electric furnace at a temperature of 700 ◦C. The ash was characterized using Energy Dispersive X-ray Fluorescence (EDXRF) and were found to possess pozzolanic properties with silica content above 70%. Cement was replaced by BLA at 5%, 10%, 15%, and 20% by weight of cement. Concrete made from these combinations were tested for compressive and splitting tensile strengths at 7, 28 and 56 days of curing. It was observed that optimum strength was attained at 5% replacement at 56 days of curing. The microstructures of the concrete revealed that at 5% incorporation of BLA in concrete, there was a better interlocking of concrete grain. It was concluded that cement can be replaced with 5% BLA in High Performance Concrete

Response Surface Methodology and Statistical Investigation of the Strength of Bituminous Sandcrete Blocks

Spalling is a serviceability related defect in buildings that degrades their appearance and if unchecked, could be a threat to building sustainability and lead to structural failures. It is associated with the effect of moisture on the building especially the blockwall. This research focuses on the production of low water-absorption Sandcrete blocks. The water absorption and compressive strength of blocks using bitumen as a coat and as part of the sandcrete mix are investigated. In assessing the outcome, eight (8) different sets of Sandcrete blocks with varying bitumen contents were defined and nine (9) samples of standard six (6) inches blocks were produced for each set, with three (3) samples per set being tested at 7,14 and 28 days for water absorption and compressive strength respectively. The water sprinkling curing method was used at 24 hours intervals. The results acquired showed that the sets that contained bitumen showed reduced water absorption rates up to 4.06% at 28 days relative to the control samples. The analysis of the experimental result was done using response surface methodology, the percentage of bitumen replacement with sand and curing days was used as the independent variable. Multiple regression equation was obtained to predict investigated properties. Further analysis of the data shows that Sandcrete blocks coated externally with bitumen give the optimum performance in terms of compressive strength and water absorption