Portland Limestone Research Articles

Application of response surface methodology in catalytic co-gasification of palm wastes for bioenergy conversion using mineral catalysts

Biomass gasification is a promising approach for bioenergy conversion. Usually, biomass gasification is facing interruption in feedstock supply due to seasonal availability of biomass. In biomass gasification, formation of tar also affects the gasification efficiency. Therefore, in this study, catalytic air co-gasification of two palm wastes (coconut shells; CS, oil palm fronds; OPF) was investigated for syngas (H2+CO) and methane production in downdraft gasifier using three mineral catalysts such as Portland cement, dolomite, and limestone to address the issues. The three main process variables were investigated within the specific range, the temperature of 700–900 °C, catalyst loading of 0–30 wt%, and the biomass blending ratio of 20–80 wt%. Response Surface Methodology, Box-Behnken Design was used for process optimization. The results showed that temperature was the most influencing parameter for syngas production, followed by catalyst loading and blending ratio. The maximum methane produced from Portland cement catalyst followed by limestone and dolomite. The syngas and methane yield was obtained 38.81 vol% and 19.96 vol% respectively at optimized conditions of catalyst loading of 20 wt%, temperature of 900 °C, and blending ratio of CS20:OPF80 using Portland cement as a catalyst. The higher syngas and methane yields from catalytic co-gasification as compared to non-catalyst co-gasification was due to the catalytic effect of Ca, Fe, Mg, K, P, and Al oxides present in catalysts and biomass materials.

The physico-mechanical influence of dehydroxylized activated local kaolin: A supplementary cementitious material for construction applications

This work presents the effect of partially replacing metakaolin with Portland limestone cement to produce mortars for construction. Teleku Bokazo kaolin was explored as a SCM in the production of mortars. The hydration product between Portland limestone and metakaolin was studied. The kaolin was heat treated to form metakaolin and partially used to replace Portland limestone cement (PLC) in mortars to explore the optimum replacement and its mechanical and durability effect. The samples were characterized using X-ray diffraction (XRD) for phases and crystallinity of the kaolin. Fourier transform infrared spectroscopy (FTIR) and Scanning electron microscopy (SEM) gave information on the functional groups formed during the hydration and structure and surface morphology respectively. The pastes and mortars produced were subjected to setting time, water absorption, flexure and compression strength test. The mechanical properties were observed to increase with increasing metakaolin replacements. Therefore, from the results obtained, it is suggested that ∼20 % replacement of Portland limestone cement with Teleku Bokazzo metakaolin can be very suitable for construction applications.

The effect of partial replacement of Nigerian Portland limestone cement with rice husk ash agricultural waste in concrete

Rice Husk is an agricultural waste which when burnt under controlled temperature, produces an ash Rice Husk Ash (RHA) owing to its rich content in silica, which is used as a super-pozzolanic material for the partial replacement of Cement in concrete. Presently, large amounts of RHA are generated in both Rural and Small-Scale Industries which has a high impact on the environment. In this work, Portland limestone cement (PLC) was partially replaced at 0%, 5%, 10%, 15%, 20%, 25% and 30% with RHA. A control of 0% PLC replacement was adopted. Compressive strength was investigated A mix ratio of 1: 1.12 : 3.07 with water-cement ratio of 0.5 was adopted for a curing period of 7, 14, 28, 60 & 90 days. The result showed that the compressive strength decreased as the percentage of RHA increased. At 90 days, compressive strength of 34.12, 29.70, 28.30, 26.67, 24.48, 23.96 and 23.42N/mm2 was recorded for 0, 5, 10, 15, 20, 25 and 30% replacement level respectively. It was recommended that further work should be investigated to check for the suitability of partial replacement of other grades of Nigerian cement with RHA in concrete.

A comparative study on the strength characteristics of Grade 25 and Grade 30 rice husk ash blended cement concrete

Rice husk ash (RHA) is an agricultural waste which is a pozzolanic material that can be blended with cement in producing concrete. This research presents investigation carried out on the comparative strength characteristics of concrete produced with grade 25 and grade 30 cement blended concrete using a replacement level of 10% rice husk ash as substitute. Two mix ratios (1:2:4 and 1:1.12:3.01) were used. A total of 60 cube size of 150mm were cast, tested and their mechanical properties determined. The RHA was made in the laboratory by burning the husk obtained from Ifo in Ogun State Nigeria using an Electric furnace, with the temperatures of the furnace at about 700°C. The results showed that the compressive strength at 28 days decreased as the percentage replacement of Portland Limestone cement (PLC) with RHA increased from 0% to 10% respectively with compressive strengths of 29.78 N/mm2 to 21.56 N/mm2 for grade 25 concrete and 32.12 N/mm2 to 26.82 N/mm2 for grade 30 concrete. It was concluded that RHA replacement in concrete can be used for the production of concrete for light structural works in the development of sustainable and green structures.

Investigating the Use of Lime Residuals as an Alternative in Portland Limestone Cement

Abstract This article presents the use of lime residuals from water treatment plants and their incorporation into concrete. Through a lime-softening process, hydrated lime is added at the water treatment plant to lower water hardness from which lime residuals form. Lime residuals are mainly calcium carbonate, which make them a good addition in cement manufacturing. Specimens were cast with lime residuals at 3 and 15 % replacement dosages to determine their potential for use in manufacturing a standard cement or creating portland limestone cement. Tests were performed on three lime residual samples and available limestone products. The results showed minimal performance differences between each of the mixtures. Fresh properties (slump, air content, and unit weight) and hardened properties along with hydration microstructure (x-ray diffraction and isothermal calorimetry) were evaluated. Results showed that the use of lime residuals could be an effective alternative for powdered limestone in portland limestone cement production. In addition, long-term external sulfate attack testing was performed. Sulfate resistance decreased with increasing lime residual content.

The influence of using hybrid polymers, aggregate gradation and fillers on moisture sensitivity of asphaltic mixtures

Abstract Moisture damage can be defined as the loss of strength of asphaltic mixtures that resulted from the presence of water. The main objectives of this research is to investigate the influence of using hybrid elastomer and plastomer polymers modifiers, aggregate gradations and mineral fillers on moisture resistance of asphalt concrete mixture. In this study, 1% and 3% of plastomer Polyvinyl Chloride (PVC) were added for both pure asphalt binder and asphalt modified with 3% of elastomer Styrene Butadiene Styrene (SBS) to form hybrid polymers. Two types of mineral fillers were used: portland cement and limestone dust with two types of aggregate gradations: fine and coarse. A Humboldt Machine was used to measure the maximum load which makes the specimens completely fractures and then to estimate the Tensile Strength Ratio (TSR). The results of the study depict that the hybrid polymers improve the tensile strength ratio. This give an indication that hybrid polymers have great effect on improving the performance of modified asphalt binder. Also, results show that hybrid polymers improve the properties of flexible pavement against moisture damage and as a result increasing the durability and the service life of the pavements. According to that, it is concluded that modifying asphalt with hybrid polymers is more preferable to be used as anti-striping. Furthermore, it is deduced that fine gradation mixtures is more resistance than coarse mixtures to moisture damage. It is also recommended to use portland cement instead of limestone dust as mineral filler material in HMA.

Performance evaluation of cashew nutshell ash as a binder in concrete production

The agro-industrial sector annually produces large volumes of waste by-products which as a result of the ignorance of their values as well as their ineffective management, pose environmental, societal and economic threats. Thus, this study explored the ash from cashew nutshell waste and replaced it with Portland limestone cement (PLC) at 5%, 10%, 15% and 20% using a mix design ratio of grade 25 MPa concrete (M 25). The cashew nutshell was sun-dried for 14 days and then burnt in a gas furnace at a temperature of 750 °C for 5 h to obtain cashew nutshell ash (CNSA). The chemical and physical properties of the CNSA were examined while the workability of the fresh concrete was investigated. Moreover, the mechanical and durability properties of the hardened concrete were carried out while the microstructures of the concrete samples were analyzed. The experimental findings revealed that CNSA met the requirements for use as a pozzolanic material. The slump and the compacting factor increased with increasing CNSA content. Moreover, both compressive, splitting tensile and flexural strengths of the hardened concrete increased as the content of CNSA increased but optimum at 15% replacement level. Furthermore, the CNSA concrete resisted more sulfate attack than the Portland cement concrete (control). The micromorphological analysis exhibited a reticular structure and adequate filling ability with the incorporation of CNSA content in the mix. Hence, it is recommended that CNSA can be incorporated as a construction material in the concrete production at the optimum replacement with PLC at 15% for structural application and 20% for non-load bearing application. This study is advantageous because fresh concrete would remain workable for longer periods, thus, resulting in the reduction of construction joints. Moreover, the utilization of CNSA concrete is also beneficial in an environment with high sulfate content. Finally, the developed model equations from this study can be used in the development of mix design of blended concrete as well as a better refinement of existing procedure of concrete mix design provided the chemical composition of the materials is established.

PENGARUH PENAMBAHAN ARANG SERBUK KAYU GERGAJI TERHADAP KUAT TEKAN MORTAR

Mortar is a mixture of adhesive (Portland cement and limestone), sand, and water with a certain composition. Mortar is used in structural and nonstructural constructions. This research uses sawdust charcoal as cement addition because in similar research mention that wood charcoal contains silica. This research was aimed to know the value of compressive strength of the mortar (1:3 and 1:5) by using sawdust charcoal as cement addition. The method of manufacture and testing compressive strength of mortar refers to SNI 03-6825-2002. The mortar specimens is cube shaped with side 50 mm and the total of specimens have 112 mortar test specimens. Variations of sawdust charcoal used were 2,5%, 5%, 7,5%, 10%, 12,5% and 15% of the weight of cement. The range of initial flow values used are 105% - 115 (SNI 03-6882-2002). The specimens were soaked for 26 days and compressive strength test of mortar was performed at 28 days. The test results showed that the compressive strength value of normal mortar (1:3) of 25,09 MPa, the value of compressive strength of variation mortar 2,5%, 5%, 7,5%, 10%, 12,5% and 15% respectively are 25,89 MPa, 26,93 MPa, 27,84 MPa, 25,58 MPa, 20,68 MPa and 17,24 MPa. The value of compressive strength of normal mortar (1:5) of 15,48 MPa, the value of compressive strength of mortar variation 2,5%, 5%, 7,5%, 10%, 12,5% and 15% respectively are 15,83 MPa, 16,24 MPa, 17,01 MPa, 15,59 MPa, 14,45 MPa dan 12,26 MPa. The highest increase of compressive strength value in mixture 1:3 was variation 7,5% by 10,94% and mixture 1:5 was variation 7,5% by 9,90% from the compressive strength value of normal mortar.

Portland limestone cement for reduced shrinkage and enhanced durability of concrete

In this work, different cementitious systems were used to investigate the shrinkage of concrete under plastic and drying conditions. Emphasis was placed on Portland limestone cement (type IL) with replacement amounts of 10% of Portland cement. Comparisons were made with a cement type with low Blaine fineness (i.e. coarse ground cement). The results indicated that type IL cement has good shrinkage results without adversely affecting other engineering properties of concrete such as strength, resistivity, degree of hydration and setting time. This is probably due to improved particle packing, access to more nucleation sites for the hydration products and the formation of calcium carbo-aluminate hydrates. Scanning electron micrographs of coarse ground cement paste also indicate a retarded degree of hydration compared to type I/II Portland cement paste.

Comparative experimental study of the mechanical and fracture properties of Portland limestone and Corsehill sandstone

An experimental investigation of the mechanical and fracture characteristics of Portland limestone and Corsehill sandstone is undertaken, aiming at enhancing understanding of the structural behaviour of these natural building stones commonly used in both new and restoration projects in Edinburgh, Scotland. A series of three-point bending and four-point bending tests on appropriately cut prismatic samples, in the presence of U-shape notches, were performed and results were interpreted following the concepts of crack mouth opening displacement and fracture energy. The critical crack opening displacement could be further investigated as a fracture criterion, in­dependently of the method used for its determination. At a second stage, the effect of specimen shape and size on flexural strength, deflection at mid-span, crack mouth opening displacement and fracture energy was studied for Port­land limestone. Despite the scattering of results, trends observed comprise (a) the negative correlation between the flexural strength of Portland limestone and the specimen span length and (b) the positive correlation between fracture energy and specimen size. Conclusions drawn are in good agreement with similar ones for other quasi-brittle materials and contribute to the assessment of the fracture behaviour of full size structural members that are often beyond the range of possible failure testing.

The Impact of Bitumen Roofing Production Waste (BTw) on Physical Mechanical Properties of Concrete

This article presents how concrete properties would change if part of a coarse aggregate (granite crushed stone) were replaced with bitumen roofing production waste (BTw). BTw is a huge ecological problem because these wastes are generated in large quantities when replacing old bitumen-based roof tiles. Wastes are also produced during the production of bituminous roof coatings. Usually BTw are stored in landfills or it is attempted to use/dispose them in the production of asphalt concrete. There are very few works which analyse the impact of BTw on the properties of cement materials, although the impact of these wastes on the properties of cement materials could be beneficial because BTw consist of aggregate, granules, bitumen and fibers. In order to use BTw, standard concrete samples were first formed, then 5/16 granite fraction was replaced with BTw in amounts of 2%, 4% and 6% by weight The amounts of limestone Portland cement, fine aggregate (sand), water and superplasticizer in the concrete mixtures were constant. The new generation of superplasticizer based on polycarboxylates was used in mixtures. The following concrete properties were identified and analyzed: density of the mixture, flowability, density of concrete samples, water absorption, compressive strength, forecasted frost resistance, and microstructure studies were conducted as well. The results of the studies showed that BTw can be used in small amounts, i. e. up to 6%, then the density of the samples slightly decreased (by 2.4%) and water absorption increased (by 0.7%). Compressive strength, after replacing 2% granite crushed stone, decreased by 2.4%. However, gradual addition of the amount of BTw resulted in more closed pores that improved the frost resistance of the concrete. When 6% of bulk filler was replaced with BTw, closed porosity, compared to control samples, increased by 54% and forecasted frost resistance - by 26%. Microstructure analysis showed that with 6% BTw a dense cement stone structure was formed, showing the hydrates of portlandite and CSH.

Effectiveness of Nanolime as a Stone Consolidant: A 4-Year Study of Six Common UK Limestones.

Protecting stone buildings from weathering and decay is a major challenge in the conservation of built heritage. Most of the stone consolidants currently available are well suited to silicate stones, but are less compatible with limestone. In this paper we present for the first time the results over a 4-year period of various consolidation treatments carried out using nanolime on 6 of the most representative and significant stones used in historic buildings in the United Kingdom. Tests investigated the influence of stone type, environmental conditions and pre-treatments on the effectiveness of the consolidation treatment. A comprehensive and rigorous testing programme was carried out to evaluate the short (12 weeks) and longer-term (4 years) effects. Stone samples were characterised before and after treatment using light and electron microscopy, sorptivity tests and a novel methodology employing drilling resistance to interrogate the near surface effects. Results show that for some of the stones, such as Clunch and Bath Stone, the positive effect of the treatment with nanolime is noticeable after 4 years since application. However, results for other stones such as Portland and magnesian limestone showed that the initial beneficial effect of the treatment is reduced after 4 years. Nanolime treatment of Ham Stone produced an unnoticeable effect on the continuous natural reduction of the drilling resistance of the specimen over time. The results presented are of immense value to conservators as they provide essential guidance on the most appropriate repair approach. Impact to the conservation industry will be to avoid the use of nanolime on stones where there is no perceivable benefit, reducing the risk of adverse effects, including potential damage to buildings. In additional costs will be saved which might otherwise have been spent on ineffective treatments.

The Effect of the Presence of Ferric Iron in Water used for the Production of Concrete on Its Compressive Strength

This study examined the effect of ferric iron inherent in mixing water on the compressive strength of concrete. Portland Limestone Cement was considered in the production of the 150mm concrete cube samples. Dirt free river sand and crushed stone with maximum size of 14mm was used as fine and coarse aggregate respectively. The water samples used for the study were sourced from the following locations as stated: Sample 1: Niger Delta University Portable water at Niger Delta University Campus, Wilberforce Island (labelled P1). Sample2: Raw water from borehole at Niger Delta University Campus, Wilberforce Island and allowed to oxidized about 3 hours. Sample 3: Raw water from borehole at Amassoma in southern Ijaw Local Area, Bayelsa state and allowed to oxidized for about 3 hours. Sample 4: Oxidized water from Ogobiri in Sagbama Local Area, Bayelsa state. Sample 5: Oxidized water from Azikoro in Yenagoa Local Area, Bayelsa state. 150mm x 150mm concrete cubes samples were prepared with the various water samples stated above. A mix ratio of 1:11/2:3 was used for this experimental study. The samples were cured in accordance with BS EN 12390-2. Compressive strength values were determined for all specimens by means of a compression testing machine. Samples were tested to failure at 7, 14, 21 and 28days. The concrete compressive strengths test results for 7, 14, 21, and 28 days for sample 1 was 24.22 N/mm2, 27.63 N/mm2, 34.04 N/mm2 and 34.59N/mm2. For sample 2 was 18.79 N/mm2, 23.55 N/mm2, 27.30 N/mm2 and 28.59N/mm2, for sample 3 was 21.12 N/mm2, 22.81 N/mm2, 25.19 N/mm2 and 26.56N/mm2, for sample 4 was 19.80N/mm2, 22.71N/mm2, 26.80N/mm2 and 27.40N/mm2and for sample was 20.89N/mm2, 21.88 N/mm2, 26.20 N/mm2 and 27.30N/mm2respectively. The test results, show a noticeable decrease in compressive strength of concrete cubes cast with water that contained ferric iron when compared with water free from ferric iron. It was concluded that Ferric iron as impurities in mixing water have significant effect on the strength of concrete.

Effect of the Presence of Ferric Iron in Water used for the Production of Concrete on Its Compressive Strength

This study examined the effect of ferric iron inherent in mixing water on the compressive strength of concrete. Portland Limestone Cement was considered in the production of the 150mm concrete cube samples. Dirt free river sand and crushed stone with maximum size of 14mm was used as fine and coarse aggregate respectively. The water samples used for the study were sourced from the following locations as stated: Sample 1: Niger Delta University Portable water at Niger Delta University Campus, Wilberforce Island (labelled P1). Sample2: Raw water from borehole at Niger Delta University Campus, Wilberforce Island and allowed to oxidized about 3 hours. Sample 3: Raw water from borehole at Amassoma in southern Ijaw Local Area, Bayelsa state and allowed to oxidized for about 3 hours. Sample 4: Oxidized water from Ogobiri in Sagbama Local Area, Bayelsa state. Sample 5: Oxidized water from Azikoro in Yenagoa Local Area, Bayelsa state. 150mm x 150mm concrete cubes samples were prepared with the various water samples stated above. A mix ratio of 1:11/2:3 was used for this experimental study. The samples were cured in accordance with BS EN 12390-2. Compressive strength values were determined for all specimens by means of a compression testing machine. Samples were tested to failure at 7, 14, 21 and 28days. The concrete compressive strengths test results for 7, 14, 21, and 28 days for sample 1 was 24.22 N/mm2, 27.63 N/mm2, 34.04 N/mm2 and 34.59N/mm2. For sample 2 was 18.79 N/mm2, 23.55 N/mm2, 27.30 N/mm2 and 28.59N/mm2, for sample 3 was 21.12 N/mm2, 22.81 N/mm2, 25.19 N/mm2 and 26.56N/mm2, for sample 4 was 19.80N/mm2, 22.71N/mm2, 26.80N/mm2 and 27.40N/mm2and for sample was 20.89N/mm2, 21.88 N/mm2, 26.20 N/mm2 and 27.30N/mm2respectively. The test results, show a noticeable decrease in compressive strength of concrete cubes cast with water that contained ferric iron when compared with water free from ferric iron. It was concluded that Ferric iron as impurities in mixing water have significant effect on the strength of concrete.

Durability of Portland-limestone cement-based materials to physical salt attack

Because salt solution ingress is governed by permeability and diffusivity and because salt crystallization pressure is directly related to pore size, changes in cement composition and hydrated microstructure may influence the durability of cement-based materials in salt-laden environments in complex ways. Here, performance of portland limestone cement (PLC) and ordinary portland cement (OPC) mortars exposed to sodium sulfate and calcium nitrate salt solutions was assessed, relative to their pore structure and sorptivity. At high w/b (0.60), increased salt crystallization damage was observed in the PLC mortar and was linked to its refined pore structure. At low w/b (0.40) performance was similar and was attributed to higher tensile strength and the inability of the salts to penetrate smaller pores. These results show that a w/b of 0.40 should provide adequate protection from capillary rise and evaporation-induced salt crystallization in both PLC and OPC mortar, but that at higher w/b differences in performance are possible.

Quantification methods for chloride binding in Portland cement and limestone systems

This paper presents a comparison of methods to quantify the chloride binding capacity for cementitious materials composed of Ordinary Portland Cement (OPC) and Limestone (LS, 0 to 55% replacement). Physical and chemical chloride bindings were investigated to better understand the binding capacity of the different systems and to provide basic information for modelling. Cement pastes samples were exposed to a 0.5 M NaCl solution and their chloride contents were quantified as free ions in pore solution, chemically bound ions in AFm phases, and physically bound ions on Calcium-Aluminum-Silicate-Hydrates (C–A–S–H). Notably, the study showed that (1) considering a solid solution between Friedel's salt and Hemicarboaluminate (Hc) was necessary for the quantification of chemically bound chlorides in limestone blended system and (2) an accurate estimation of the C–A–S–H content was critical for quantifying physically bound chlorides.

St Michael’s, Tilehurst: geological developments since the Enlightenment in a rural-to-urban graveyard in central Berkshire

ABSTRACTDivided into unequal parts by New Lane Hill, the large graveyard at St Michael’s Church makes a substantial contribution to the landscape of Tilehurst, an independent medieval settlement episodically absorbed into the modern town of Reading as it grew westward. Memorialised burials began here in the eighteenth century and continued without a break at an increasing rate up to the present. A total of 2,446 memorials (ashes burials excluded) can now be seen, of which 300 (12.3 per cent) cannot be dated, mainly for preservational reasons. A wide variety of geological and some artificial materials have been used for memorials. The most prevalent of British origin are Cornubian granites and Portland stone, the latter from the earliest burials onward. The most prevalent rocks from overseas are Italian marble, generic granites, diorites-gabbros, and microgabbros. Minor use was made of Scottish granites (Aberdeen, Peterhead), Upper Carboniferous sandstones (including Millstone Grit and Pennant sandstone), generic limestones (including Nabresina and Lower Carboniferous limestones), Norwegian larvikite, slates, and gneisses/ migmatites. The seldom-used artificial materials include terrazzo and concrete. These various materials appear in the graveyard in a well-defined temporal sequence that reflects successive, cost-reducing advances in national and international transport (turnpike roads to shipping freight containers). Changes in local taste over time are reflected in the design of the monuments, ‘Georgian’ headstones giving way to Gothic, in turn replaced by art deco, and then modern. The rate of memorialisation fell during historical periods of economic hardship, when non-essential goods and services were less affordable. The Napoleonic Wars, the Great Agricultural Depression, and the two World Wars are all recognisable in the temporal pattern of dated burials as relative wealth fluctuated.

Preparation and properties of Portland limestone cements

Limestone is a suitable substitute for economically less favourable Portland clinker in Portland blended cements. Limestone in cement not only serves as a very fine filler, but can also act as a reaction component. In this work, the properties of laboratory Portland cements with limestone were studied. The cements were prepared from two limestone types and two clinker types with a graded limestone content of up to 30 wt. %. The limestones had a different CaCO3 content. Clinkers were distinguished by a marked difference in C3A content and hydraulic activity. The effect of limestones on the technological properties of cements, the hydration process and the impact of separate and together grinding of limestone and clinker were studied. In this case, the type of clinker had stronger impact than the type of limestone on the technological parameters. It was also confirmed that a low limestone content has a positive effect on cement hydration.

Response of concrete to cyclic environments and chloride-based salts

The shift towards performance-based standards and specifications for concrete requires the development of holistic tests that better correlate to field conditions, which can reliably evaluate the performance of normal and emerging types of concrete. In the current study, the response, in terms of physico-mechanical properties and microstructural features, of concrete made with different types of cement (general use [GU] and Portland limestone cement [PLC]) without or with fly ash and nanosilica to chloride-based de-icing salts (individual and combined) was assessed when cyclic environmental conditions were considered. The results revealed the coexistence of complex deterioration processes in concrete under this combined exposure. The combined salt (MgCl2+CaCl2), which simulates using a synergistic maintenance and protective strategy for concrete in cold regions, was the most aggressive solution. PLC concrete mixtures exhibited better resistance to de-icing salts compared to GU mixtures due to synergistic physical and chemical actions of limestone in the matrix. The incorporation of 30% fly ash had a pronounced effect on improving the durability of concrete to the combined exposure, and this performance was much enhanced when nanosilica was incorporated in the cementitious system.

Causes of failure in concrete elements buried in lagoon water

The effect of salt attack on reinforced concrete structures in marine environment has become a source of concern to stakeholders in the construction industry. This trend has led to cracks and sometimes failure of structural members that are exposed to this environment. This study investigated the strength performance of concrete elements in lagoon water which is an offshoot of the Atlantic Ocean in Lagos State, Nigeria. A total of ten 150 mm cubes, and ten 150 mm × 150 mm × 600 mm reinforced concrete beams were cast using Portland limestone cement of 42.5-R at 28 days strength of 40 N/mm2 and cured in both fresh and Lagoon water with water-cement ratio of 0.45. Chemical analysis were carried out to determine the concentration of ions. Mechanical tests were also carried out on the concrete elements. The chemical analysis result showed that Calcium (Ca) was the predominant element having 61.62% in the concrete sample cured with lagoon water while concrete sample cured in fresh water had 51.77%. The flexural behaviour of reinforced concrete beams showed that the flexural stiffness of beams were 15.1 N/mm2 and 12.46 N/mm2 in the lagoon and fresh water, respectively. The compressive strength of concrete cubes cured in fresh water was 42.67 N/mm2 while that of lagoon water was 34.22 N/mm2. The preliminary results showed that concrete gained strength at the early stage for reinforced concrete beams buried in the Lagoon and reduced in strength at the early stage for concrete cubes buried in Lagoon. The result of the compressive strength showed that the high presence of salt could have contributed to the cracks and eventual spalling of concrete elements in marine environment.