Assessment of Selected Dams in Kwara State, Nigeria

In Nigeria, more than 50% of the geographical area lies in the Savannah. Over time, this area has been vulnerable to the vagaries of periodic and severe droughts, affecting the survival of man and animals. Safe and economic design and construction of dams to store surplus river waters thus assumed greater urgency. However, dam failures and flood issues has caused catastrophic damages and losses of lives and properties. The uncertainties associated with deteriorating dams have necessitated proper and timely assessment and rehabilitation of these structures. This study identifies and investigates relapse in four (4) selected dams in Kwara State namely: Unilorin-, Malete-, Okuta- Oja- and Asa-dam. A series of field inspection was carried out and results obtained were analyzed. Amongst the four dams, Okuta-Oja dam displayed the worst case of relapse with seepages through the foundation and body of the dam. About 20 baffle blocks out of 30 have been damaged in Unilorin dam, while Malete dam was undergoing re-construction owing to seepage failure. Asa dam however remains intact with no physical and structural defect. Unless appropriately handled, ageing and relapsing infrastructural systems can pose a significant problem, threatening economic prosperity and public safety. Thus, monitoring the state of dam structures to ensure timely maintenance is critically important to preventing catastrophic disasters

Interaction assessment and optimal design of composite action of plastered typha strawbale

The concept design of the typha strawbale masonry came up as a result of the urgent demand for a means of constructing sustainable buildings, both in rural and urban settlement, not only suitable for dwellers but for keeping farm products by structures that will respond to the environmental eco-system, coupled with the fact that such structures are also affordable, durable and easy to maintain during their service period. The effects of contact between plaster and the stacked strawbale of a masonry needs to be established and design optimization for durability and stability of the masonry be obtained. The assessment will involve the application of plaster materials (cement and natural earth) to the wall specimen panels. Past works have shown that plastered strawbale walls have adequate resistance against the appropriate vertical loads, and further showed that the earth plaster can bear higher stress than the cement plastered straw bale. There is the implication that the collapse or response of the earth-strawbale wall is significantly higher compared to that of cement-strawbale from other straw-based masonries. Therefore the allowable stresses of plastered typha strawbale shall be predicted for their optimum values using SAP2000. The stress stability of each masonry is obtained by analytical model using the best fit variables for the wall height and thickness

Experimental Study on the Workability of Self-Compacting Granite and Unwashed Gravel Concrete

This study deals mainly with the mix proportions using granite and unwashed gravel as coarse aggregate for self-compacting concrete (SCC) and its workability, by considering the water absorption of unwashed gravel aggregate. Mix proportions for SCC were designed with constant cement and fine aggregate while coarse aggregates content of granite-unwashed gravel combination were varied in the proportion 100%, 90%/10%, 80%/20%, 70%/30%, 60%/40%, 50% /50%, represented by SCC1, SCC2, SCC3, SCC4, SCC5 and SCC6. 100% granite (SCC1) serves as the control. The workability of the samples was quantitatively evaluated by slump flow, T500, L-box, Vfunnel and sieve segregation tests. Based on the experimental results, a detailed analysis was conducted. It was found that granite and unwashed gravel with SCC1, SCC2 and SCC3 according to EFNARC (2002) standard have good deformability, fluidity and filling ability, which all passed consistency test. SCC1, SCC2 and SCC3 have good passing ability while all mixes were in the limit prescribed by EFNARC (2002). It can be concluded that the mix design for varying graniteunwashed gravel combination for SCC presented in this study satisfy various requirements for workability hence, this can be adopted for practical concrete structures

INFLUENCE OF GRANITE-GRAVEL COMBINATION ON THE STRENGTH OF SELF-COMPACTING CONCRETE: TOWARDS A SUSTAINABLE CONSTRUCTION MATERIAL

This study focusses on the influence of granite-gravel (washed and unwashed) combination as coarse aggregate on hardened properties of Self-Compacting Concrete (SCC). Granite-gravel combination in varying percentages was used as coarse aggregates to produce SCC while other concrete constituents were kept constant. The experiments executed on hardened SCC were compressive and split tensile strength. Concrete were made using 150 mm cubes and 100 mm × 200 mm cylinders. Data obtained were analysed using graphical illustrations while Minitab was used to model values for the mix proportions. The compressive strength of SCC produced reliable results with a minimum strength of 30.96 N/mm² for 50% washed gravel at 28 days of which, the strength also increases as curing age increased. The split tensile strength of SCC increases as the curing day increased but decreased as gravel content increased with 50/50 threshold limit. The Surface plots analysis shows that the percentage increase of granite-washed gravel combination as coarse aggregate and curing ages in SCC has significant impact on compressive strength. It can be concluded that granite/gravel combination as coarse aggregates in SCC production is feasible and reliable provided the threshold limits of 50% washed gravel and 30% unwashed gravel are not exceeded

EXPERIMENTAL STUDY ON THE DURABILITY TO SALINE ENVIRONMENTS OF SELF-COMPACTING CONCRETE MADE WITH COARSE AGGREGATES COMBINATION

This study focus on durability to saline environments of self-compacting concrete (SCC) made of granite-gravel combination as coarse aggregates in concrete production. In this study fine aggregates, water, superplasticizer and cement were kept constant. The percentages replacement of gravel in place of granite aggregates were 10, 20, 30, 40, and 50, while 100% granite serves as control. A total of 162 cubes of 100 100 100 mm concrete specimens were immersed over the initial curing in a water container and further cured in 5% sodium chloride (NaCl) and sodium carbonate (Na2CO3) solutions for 28, 56 and 91 days in line with ASTM C39 (2003). The tests results indicate that concrete cured in five percent (5%) of NaCl solution have compressive strength accelerating properties at early age that could not be sustained for long. While those cured in 5% of Na2CO3 solution reduced significantly the compressive strength of concret

Optimization of Calcined Beans Pod Ash – Cement Blended Concrete Mix Using Taguchi Method

This study investigated the optimization of calcined beans pod ash (BPA) - cement concrete mix using the Taguchi method. Concrete is a widely used building material with various performance requirements. These requirements are mostly influenced by concrete constituent materials and mixtures proportion obtained from concrete mix design. But improper mix design can result in inherent defects or local imperfections, which can significantly deteriorate the performance properties of concrete and jeopardize the structural integrity and durability of concrete structure. Taguchi method of optimization was employed to address these challenges. It involves identifying key factors (water – cement ratio, percentage of BPA – cement replacement, fine to total aggregate ratio and super-plasticizer dosage), selecting suitable levels for these factors, and conducting experiments to determine the optimum combination of factors. The effects of these variables on concrete slump flow (SF), compressive strength (Fcu), and split tensile strength (Fy) were evaluated. The results of SF, Fcu and Fy of BPA – cement concrete show significant improvement of 23.74%, 21.72% and 21.43% respectively, when cement was partially replaced with BPA from 5% to 20%. Likewise, an improvement of 5.97%, 5.69% and 5.37% for SF, Fcu and Fy of BPA – cement concrete, when the dosage of super-plasticizer in concrete mix was varied from 6% to 12%. A respective optimal parameter combination for BPA – cement concrete slump and strengths were obtained at 0.40, 5%, 0.4, 6 ml/kg of cement and 0.35, 5%, 0.4, 6 ml/kg of cement for W-C, BPA, F-T Agg, SP respectively

PSEUDO-DYNAMIC EARTHQUAKE RESPONSE MODEL OF WOODFRAME WITH PLASTERED TYPHA (MINIMA) BALE MASONRYINFILL

This study looks at designing and evaluating strength of typha strawbale wall cross section rather than the assumption of edge column acting as axially loaded members that should resist all vertical members from the loads acting on the wall. Based on the aforementioned claim, the objective of this work is to provide the average design thickness for the cement-plastered typha strawbale that stiffens the wooden frame. Data on strength and deformation of the structure are the input for the analytical models. Pseudo-dynamic earthquake response tests, of a one quarter (¼) scale model low rise storeys wooden frames stiffened with cement plastered strawbale masonry was conducted. The structure is idealized as plane frames. The analysis utilised the hysteresis models for members' models as time-independent. The force-displacement relationship of the members' models has been evaluated by the approximate method on the basis of the material properties and structural geometry. A model was investigated with straw bale infill panel to determine the hysteretic parameters, stiffness deterioration and strength degradation due to seismic forces

Reliability assessment of ground granulated blast furnace slag/ cow bone ash- based geopolymer concrete

This study focused on the reliability assessment of ground-granulated blast furnace slag (GGBS) and cow bone ash (CBA) based geopolymer concrete (GPC). To produce the GPC, sodium silicate (Na2SiO3) was mixed with sodium hydroxide of 12M at a 2.5:1 ratio and used as the alkaline activator. The mechanical properties of the GPC were examined at 7, 14, 28, 56, and 90 days of ambient curing. Microstructural analyses were also carried out to investigate the microstructural properties that influence the mechanical performance of the GPC. Following these, a reliability assessment was carried out to establish the reliability of GPC using the constant failure model method. The results of the mechanical tests showed that GPC with GGBS composition that is ≥ 60% and CBA that is ≤ 40% performed better than the conventional concrete. At 28 days of curing, the GPC optimum mix attained a compressive strength of 40.13 MPa against 33.14 MPa attained by the conventional concrete. Also, the reliability analyses established that GPC mixes with GGBS composition that is ≥ 60% and CBA that is ≤ 40% are reliable up to the expected 50 years of service for structures. Hence, GPC is reliable as well as conventional concrete

Assessment of Gravel Properties Sourced within Oyo North Senatorial District: Case Study of Ogbomoso

The study evaluated the properties of gravel aggregate sourced within Oyo north senatorial district for concrete production in place of crushed granite crushed at exorbitant cost since characteristic properties show significant reflections on the qualities of gravel aggregate used and also play major role in determining the properties of hardened concrete. Samples of gravel from four commonly used borrow pits: Aroje, Bolanta, Sunsun and Olomi sites were obtained and tested for Aggregate Crushing Value (ACV), Aggregate Impact Value (AIV), Specific Gravity, Water absorption Capacity, Bulk Density, Moisture Content and Particle Size Distribution. On the average the results of the observation for the selected four locations were 22.56 g, 28.17 g, 33.37 g and 40.19 g for Aggregate Crushing Value (ACV), 2.44 g/ml, 2.53 g/ml, 2.57 g/ml and 2.62 g/ml for Bulk density, 0.17 %, 1.43 %, 2.42 %, and 2.48 % for moisture content, 2.02 %, 2.92 %, 2.00 % and 3.15 for water absorption, 2.52, 2.63, 2.60 and 2.55 for specific gravity, 41. 55 %, 45.25 %, 45.59 % and 47.08 % for aggregate Impact respectively. The study revealed that, gravel aggregates from Aroje has superior properties over those of Sunsun, Bolanta and Olomi as compared with coarse aggregate properties in BS 812: 1995 and BS 882: 1992. It is hereby recommended for coarse aggregate in concrete production

EXPERIMENTAL AND MODELLING OF FLEXURAL STRENGTH PRODUCED FROM GRANITE-GRAVEL COMBINATION IN SELFCOMPACTING CONCRETE

The roles of coarse aggregate in concrete production cannot be over emphasized because of the volume coarse aggregate occupied in total concrete volume. The availability of locally sourced gravel aggregate (both washed and unwashed) but not put to optimal use called for this current study. The granite-gravel aggregates were varied in percentage proportions of 100/0, 90/10, 80/20, 70/30, 60/40, 50/50. A total number of 108 beams of 100×100×500 mm size were produced and cured for 28, 56 and 91 days, crushing of beams were done in line with the standard to determine the flexural strength. The MINITAB software was used to model the concrete produced. The test results indicate that 100% granite and granite-washed gravel combination up to 30% behaves satisfactorily in the reinforced concrete structure using self-compacting concrete while 40 and 50% for washed gravel showed a bit of satisfactions. Similar trend was observed for unwashed gravel of which flexural strength of the beam is still reliable at 40% unwashed gravel