Browsing by Author "Nanayakkara, SMA"

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item: Conference-Abstract
Analysis of the effect of wind on façade fire propagation through computational fluid dynamics modelling
(Department of Civil Engineering, Faculty of Engineering, University of Moratuwa, 2022-12) Gunarathne, GKUS; Rathnayaka, S; Weerasinghe, TGPL; Nanayakkara, SMA; Mallikarachchi, C
Façade fires are one of the most critical and increasingly frequent hazards in buildings. These fires pose a great risk to the building occupants. The Grenfell Tower fire, which happened in 2017, killing 72 people, is one of the deadliest façade fire incidents. Events like these emphasize the importance of studying the nature of façade fires. Façade fires can spread quickly through the full height of the building. Also, these fires can spread into nearby structures. Researchers have identified several factors that affect façade fire propagation. The main factors include façade material, cavities, geometry of the building, and wind. The focus of this study is the effect of wind on façade fire propagation. Building standards have set requirements to ensure the fire safety of façades. A large-scale façade fire test is one of the methods that building standards have used for this purpose. There are several large-scale façade fire test types in different countries, and the nature of these tests varies significantly from one another. One common theme in all those tests is that they do not consider the effect of wind. Therefore, even though the façades are designed according to the building standards, there is an unforeseen risk in fire situations when the wind is present. This study tries to address that limitation by numerically modelling a large-scale façade fire test and assessing the effect of wind. Fire Dynamic Simulator (FDS) was selected as the numerical tool. FDS is a Computational Fluid Dynamics (CFD) software for fire-driven fluid flows. First, a validation study was performed by numerically modelling a large-scale façade fire test that was conducted in a fire test facility in Melbourne. The experimental setup was 18 m tall, and thermocouples were placed at 10.5 m, 13.5 m and 16.5 m heights to record the temperatures. Wind speed and direction were measured at a height of 10 m. The test specimen consisted of two façade materials: an aluminium composite panel (ACP) with a combustible polyethylene core and a completely non-combustible profiled aluminium panel. The ACP panels consisted of a 4 mm polyethylene core sandwiched in between two 1 mm thick aluminium sheets. These materials were simulated in the numerical model using the material properties gathered from literature and product-specific data sheets. The total dimensions of the numerical domain were 22.4 m x 20.8 m x 19.2 m (length x width x height). This domain was large enough to account for the whole test, the fire plume resulting from the combustion, and the turbulences due to wind. Monin-Obukhov similarity theory was used to model the wind inside the numerical domain. The thermocouple results were extracted from the numerical model, and they were validated using the experimental results. The flame behaviour of the numerical model was compared with that of the experiment for further validation. After the validation, the effect of wind was examined through further numerical modelling. It has been shown that wind has a significant impact on façade fire propagation. The façade fire spread decreases with increasing wind speed when the wind direction is parallel to the main wall of the test specimen. Wind direction also impacts fire propagation. Findings from this study highlight the importance of considering wind in façade fire safety, especially in large-scale façade fire tests.
item: Conference-Abstract
Applicability of rcpt for performance-based durability design of reinforced concrete structures
(Department of Civil Engineering, 2023-09-27) Abeywickrama, HM; Nanayakkara, SMA; Mallikarachchi, C; Hettiarachchi, P; Herath, S; Fernando, L
Concrete is an extensively used composite material in the construction industry, known for its heterogeneous nature. In the context of structural service life predictions, the durability of concrete plays a vital role, especially with the advancement of new constituent materials. Among various factors contributing to concrete deterioration, corrosion of reinforcement poses a significant challenge to durability. Chloride ingress is one of the primary factors that cause corrosion of reinforcements. Therefore, this research paper focuses mainly on the impact of chloride-induced corrosion which is the major cause of corrosion of reinforcement. There are several tests that are still available to evaluate that kind of corrosion. The Rapid Chloride Penetration Test (RCPT) serves as a quick measure of chloride ion penetration resistance, which relies on the characteristics of pore structure and pore solution. The standard RCPT (ASTM C1202) is done under certain conditions. But there are limitations and drawbacks of RCPT due to certain conditions. In that way, the significant effect of RCPT results can be evaluated by changing the voltage, cathodic solution, and time. Therefore, this study investigates the influence of the cathodic solution changing with natural seawater to represent more actual conditions. The chloride content of that seawater was 10% w/w. The standard RCPT gave 2401 C while the modified method gave 3122 C as the charge pass. Once the RCPT procedure concludes, concrete powder samples were collected at various depths to determine the chloride profile. These obtained profiles were then subjected to nonlinear regression analysis to calculate chloride penetration depths. By applying Fick's second law to the chloride profile and penetration depth, the chloride diffusion coefficient was determined. Finally, a performance-based design approach was proposed, linking RCPT values with the Fib Model Code 2010, to predict the service life of uncracked concrete affected by corrosion. Then results were compared with the results which were obtained by a standard method for chloride diffusion coefficient. That standard method used for this study was RCMT (according to NT BUILD 492). Then the obtained diffusion coefficient values were 21.43 mm2/year, 20.97 mm2/year, and 21.02 mm2/year for the standard RCPT, the modified method and the RCMT, respectively. The errors were 0.2% and 1.9%, for the modified method and standard RCPT when compared with RCMT result. On the other hand, the predicted service lives for standard RCPT and modified methods were 44.32 years and 42.84 years, respectively. The RCMT gave the service life as 40 years. So, the percentage in errors were 10.8% and 7.1% for standard RCPT and modified methods when compared with RCMT result. In conclusion, standard RCPT should be modified by using sea water from actual environment instead of 3% NaCI solution if the structure is contact with sea water. RCPT can be used for performancebased durability designs. However, further investigations are required to establish the correlation between RCPT values and chloride diffusion coefficient for different grades of concrete.
item: Thesis-Abstract
Application of roller compacted concrete for road pavements in Sri Lanka
Ekneligoda, TC; Nanayakkara, SMA
There is a great need to construct more durable roads such as concrete roads in Sri Lanka since the government is spending a considerable amount of money every year to maintain the national road network which has been constructed using with either conventional asphalt concrete or bituminous paving materials. This research was carried out mainly to explore the possibility of introducing more durable and cost effective Roller Compacted Concrete for road pavements in Sri Lanka. The structural behavior of Roller Compacted Concrete pavement (RCCP), which is a rigid pavement, is completely different from conventional asphalt pavements which are designed as flexible pavements. Since RCCP is not currently used in Sri Lanka there is no local standards available for design and construction of RCCP. An extensive literature review was carried out regarding the design of rigid pavements practiced in other countries. The rigid pavements can be designed using different types of design methods for given conditions. However, out of those methods, American Association of State Highway Traffic Organization method (AASHTO) and Portland Cement Association (PCA) method are popular in the countries where rigid pavements are used. Out of these two methods AASHTO method uses more parameters in designing the pavement thickness. Therefore, parametric study was carried out to investigate the effect of each parameter used in AASHTO method. And also a computer program was developed based on PCA method to carry out the thickness design procedure effectively, as it is more suitable for low volume traffic conditions. An experimental investigation was carried out to formulate a mix design procedure for RCC using local materials. Since the thickness of RCCP depends on the flexural strength of RCC, tests were carried out to investigate the factors affecting the flexural strength of RCC and also other properties such as wet density, compressive strength and drying shrinkage. New test methods were developed to measure these properties specially the flexural strength and wet density incorporating actual conditions of RCC such as actions of static and vibrating rollers. A new apparatus was developed to measure the wet density by modifying the conventional V-B apparatus where vibration as well as known static pressure can be applied to compact concrete. Furthermore, use of chemical and mineral admixtures to improve the properties of RCC was also investigated. Based on the results of experimental investigations a mix design procedure for RCC was proposed.
item: Thesis-Abstract
Blast resisting concrete walls
Indiketihewage, KN; Nanayakkara, SMA
Today people around the world wake up, eat, live and sleep with terrorism. It has become a global menace. As a citizen lives in a country hit by a civil war for over three decades gave me motive and courage to set off this project. The project was basically planned to carry out in two parts, i.e. the literature survey and the experimental investigation. Initially a comprehensive literature survey was carried out to cover the several areas./ As terrorism is the main reason to for this project to exist, the literature survey was started off with an insight view of terrorism, its motives, methods and objectives of terrorist organisations. Later the survey was expanded to explosives and weapons frequently used by the terrorists. At the next stage of the literature survey, a review was done on the existing knowledge of blast resisting designs followed by a study on the various structural responses to blast loadings. The literature survey was further extendedto design of blast resisting structures and finally to design of elements to resist blastloadings was also completed. As a measure to increase the resistance to blast loadings, important characteristics of steel fibre and welded meshes were also studied./ The experimental investigation of the project was directed to find solutions to two situations, in battle field or terrorist attack. First series of tests of the project were concentrated on close range high explosive detonations./ Unfortunately, this part of the project had to be abandoned due to unavailability of TNT explosives in slab form. This brought to the abrupt end to the test series one of the project./ The second series of tests were focused more on a military situation, where terrorist fire with RPG 7 at bunkers. After the testing, it was revealed that the designed concrete panel might barely withstand the RPG 7 fire. The reason for this may be the fact that the effects of small steel balls were not considered in the design. Only the amount of explosives and the distance from the centre of the RPG 7 mortar to panel were considered
item: SRC-Report
Bond and compressive strength of masonry for locally available bricks
Konthesinghe, KMC; Jayasinghe, C; Nanayakkara, SMA
The bond between brick and mortar plays an important role in the ability of masonry to resist loads. The single and most important property of mortar is bond strength, and it is critical that this bond be complete, strong, and durable. The mechanism of bond between masonry units and mortars is known to be influenced by large number of factors. This paper presents an outcome of a study conducted on tensile and shear bond strength of masonry and compressive strength of masonry. It was also investigated to develop a possible relationship between shear and tensile bond strength. An experimental program was conducted to determine the impact of bond strength on compressive strength of masonry. Tensile bond strength was determined by testing brick couplets and shear bond strength by testing triplets as recommended in relevant standards. Wall panels were tested to find out the compressive strength of masonry. The effect of deferent factors such as grading of sand, soaking time of bricks and type of bricks on the bond strength as well as the compressive strength of masonry’ was found. The outcome of this research will have a higher benefit to the construction industry where masonry structures form a substantial portion.
item: Thesis-Abstract
Comparison of prestressed and reinforced concrete ground reservoirs
Fernando, KMNS; Nanayakkara, SMA
There is a great demand for new pipe borne water supply schemes as well as expansion of existing pipe borne water supply schemes due to rapid urbanization, industrialization and host of other reasons demanding construction of more and more ground reservoirs to feed water to meet these water supply needs. Traditionally, ground water storage reservoirs have been built out of reinforced concrete and most of them are rectangular in shape with a few being circular. In Sri Lanka only two pre stressed ground reservoirs have been constructed, one in Galle Water Supply Scheme in Beak and the other one is for Greater Colombo Water Supply Scheme in Maligakanda having capacities of 2.0 and 3.0 million gallons respectively (9000 m3& 13,500 m3)./ The land and space available for construction of ground reservoirs in urban areas becoming less and less and construction materials such as cement, aggregates, reinforcing steel and skilled labor etc becoming scarce and construction of prestressed ground reservoir could offer a solution to these problems./ Based on data collected on some of the ground reservoirs already constructed in Sri Lanka it could be seen that the prestressed concrete reservoirs could offer economical solutions when compared with reinforced concrete construction with respect to the usage of land and construction materials due to structural configuration and the ability of prestressing to reduce concrete sections./ A major draw back in the prestressed reservoir design is its inability to adapt to the land shape due to shape restriction to circular only and also lack of experienced contractors in prestressed construction presently in Sri I.anka. The selected structural arrangement for the dome roof consists of spherical dome roof with shell structure with prestressed ring beam resting on a rubber pad which is resting on the top of the wall.
item: Thesis-Abstract
Comparison of shell element forces obtained through classical analysis and computer software
(2015-09-17) Vithanage, SC; Nanayakkara, SMA
The “intze” type water tanks are economical for storing large capacities of water. Therefore accurate analysis of these structures is essential. Modern trend is to use computer software for analysis and design of structures. It is easy and time saving. There are many commercial software available for the structural analysis. However, the accuracy of the output of the software depends on how well the actual structure is modeled. All those software are finite element based. There are many types of finite elements developed for the purpose of structural modeling. These elements have their own advantages and limitations in different situations. Selection of correct type of element and proper fineness of mesh is very important in achieving accurate results. The aim of this research is to study the proper type of finite element and the optimal fineness of mesh suitable for different types of shells. In this context, the results obtained using different type of finite elements and different fineness of mesh used for analysis of “intze” type water tower were compared with the results obtained through classical analysis. A 1500m3 intze type water tank was selected as a structure to analyse and compare the results. First, the structure was analyzed using elastic theory of thin shells with certain approximations. Stress analysis of “intze” tanks is extremely complicated due to many degrees of redundancies. The computer software “STAAD Pro” was used for the finite element modeling of the tank. Initially 2-noded beam elements and 4-noded plate bending elements were used to model the structure. Many different models were created modifying the initial model until a result which is well comparable with classical results is obtained. Following models were created in “STAAD Pro”, Model 1. Beams were modeled as 2-noded beam elements and shells were modeled as 4-noded plate bending elements. Model 2. Vertical axis and horizontal axis bending moments were released from the 1st model. Model 3. Actual member eccentricities were given for the beams in 2nd model. Model 4. Both beams and shells were modeled as 4-noded plate bending elements. By comparing the results of above 4 models with results obtained through classical analysis, most suitable model was identified. After identifying most suitable model representing the structure, following further studies were carried out. Model a) Use of 3-noded shell elements instead of 4-noded shell elements. Model b) Changing the fineness of the mesh to study the effect of element size in final results. The results obtained were studied and made a conclusion on the suitability of different types of finite elements for different types of elements. It has been found that the STAAD Pro model 3 is the better structural representation of actual structure. STAAD Pro model 3 is the model which has vertical and horizontal axis bending moments released and actual eccentricities were given at the member start node and end node of the ring beam elements. Shells are quadrilateral plate bending element as 4 nodes of the plate in every shell lie on same plane.
item: Conference-Abstract
Construction and demolition waste as a road construction material in rigid pavement design
(2008) Gayani, JKU; Kumara, MAW; Nanayakkara, SMA
This paper focus on investigation of properties of recycled aggregate and use of recycled concrete aggregates to partially or fully replaced natural aggregates in the production of lower grade concrete. Recycled products may reduce the demands for new materials. Among which recycled aggregate (RA) is one of the major construction waste capable of being reused in the production of concrete. To evaluate the viability of this process, an experimental campaign was implemented in order to monitor the mechanical behavior of such concrete. With aim of that, the recycled aggregate properties were evaluated at the beginning before utilizing them in concrete application. The obtained test results in assessing properties of aggregate are reported in terms of (i) particle size distribution; (ii) particle density; (iii) porosity and absorption; (IV) particle shape; (v) strength and toughness.
item: Conference-Abstract
Cracking in concrete structures due to delayed ettringite formation
Nanayakkara, SMA
This paper presents a review of concrete deterioration due to delayed ettringite formation (DEF) including available test methods and guidelines to prevent deterioration of concrete due to DEF. Recently. severe cracking in some of the pile caps of bridge piers in the Southern Highway project was reported After extensive investigations, if was found that the main cause for cracking in those pile caps was DEF. DEF is sometimes referred to as internal sulphate attack which is an internal swelling reaction of the concrete that occurs in the presence of water without any external ingress of sulphate. Often DEF is associated with other deterioration mechanisms such as aggregate silica reaction (ASR). Crack pauern due to both DEF and ASR are very similar and therejore it is difficult to identify the exact cause jor cracking without carrying out petrographic and SEM studies oj the affected concrete. Cracking due to DEF was originally reported in steam-cured concrete railway sleepers bUI it can also occur in large concrete pours where care temperature can be very high as a result of heal of hydration It is widely accepted that concrete subjected 10 high temperature (> 70 °C) at early age and exposed to moisture continuously or intermittently after concrete has hardened is likely to crack due to DEF. Therefore this problem can occur in thick concrete members like pile caps. deep beams. bridge piers and raft foundations. II was reported that the composition of cement especially C3A. SO) and alkali content can contribute to DEF induced cracking. II was also reported that apart from controlling maximum temperature rise in concrete and composition of cement, use of fly ash or slag blended cement is also effective in preventing cracking due 10 DEF.
item: Thesis-Abstract
Design of cost effective composite reinforced brick work-ferro cement water tanks
Ranawaka, RATN; Nanayakkara, SMA
In Sri Lanka, the most of the farmers are in dry rural areas and due to lack of water they can't cultivate in an effective manner. Therefore, there is a great need of designing and constructing of water tanks for rainwater harvesting purposes. This research was carried out to formulate design and construction of water tanks by using low cost materials with easy methods of construction and sufficient strength. Then water tanks can be constructed as fully underground, partially under ground as well as above ground, tanks. Since Sri Lanka is developing country and these tanks are going to be constructed in the rural area, the construction method should be cost effective as well as simple. Ferro-cement is low cost material and it does not require some formwork like in concrete. And also it does not require skilled workers and supervision and also the maintenance is very much easy. The design is based on analytical results obtain from a computer programme. An experimental investigation was carried out to find the properties of the construction materials required for the design. The computer programme had been already developed for the two types of water tanks, which are cylindrical tanks with spherical roof and flat bottom and cylindrical tanks with spherical roof and spherical bottom. This computer programme was further developed to analise the cylindrical tank with conical roof and spherical bottom. All the tank types can be analyzed using this software for fully under ground, partially under ground and above ground tanks. The linear elastic theory of shells is used to develop this programme. The optimum dimensions for the water tanks, which gives the highest strength can be found by using the computer programme. It was found that there are three main parameters, which influence to the combined stress in the tank. The main parameters are, limiting angle of the spherical roof, limiting angle of the spherical bottom and radius of cylindrical tanks. The sensitivity analysis was carried out by varying only one parameter at a time while keeping all the others constant. The analysis was done for all the load cases. According to the results of the parametric study, optimum tank shape was selected for 25m3 capacity tank. The structural design was carried out for the optimum tank shape. A construction process is also presented for the selected tank shape.
item: Thesis-Full-text
Design of Dowels for shear transfer at the interface between concrete cast at different times : a case study
Karunarathna, SMP; Nanayakkara, SMA
Enlargement of original cross-sections or replacement of defective concrete layers with new concrete are usual situations in strengthening operations of reinforced concrete structures. In these situations, the shear strength between concrete cast at different times is crucial for the monolithic behavior of the strengthened members. Most design standards for concrete structures present design procedure for estimating the shear resistance between concrete layers based on the shear friction theory. The study includes three-dimensional and two-dimensional finite element model (FEM) analysis for calculation of shear stresses and comparison of three different code approaches, i.e. BS8110, ACI 318 and EN 1992, for determination of design shear resistance at an interface between concrete cast at different ages of a pile cap supported on precast concrete piles. Based on the results of the analysis carried out, it can be stated that complicated three dimensional finite element model analysis is not always essential for analysis of structures, which are having complex geometrical shapes. It is possible to transform three-dimensional problems to a simplified two-dimensional problem based on the level of accuracy required. For the selected surface characteristics and r/f percentage, the estimated design shear resistance based on recommendations of EN-1992-1-1-2004 was found be lower than the corresponding estimated value based on ACI 318M-11 recommendations. It was further observed that BS 8110-1-1997 recommendations gives the highest value for the design shear resistance independent of r/f percentage provided. EN-1992-1-1-2004 can be used to compare contribution of concrete interface roughness and interface reinforcement on design shear resistance without any limitation of design shear stress as specified in ACI 318M-11. Furthermore, the EN-1992-1-1-2004 recommends a conservative value for design shear resistance compared to other two standards.
item: Conference-Abstract
Design of rigid pavement joint spacing for rural roads.
(Department of Civil Engineering, 2011-07) Karunarathne, AMAN; Mampearachchi, WK; Nanayakkara, SMA; Pasindu, HR
When it is compared with the flexible pavements, tensile stresses along the pavement layers are more significant in rigid pavements. Shrinkage stresses and thermal stresses are the dominant contributors to develop the tensile stresses in rigid pavements. Providing lateral joints in appropriate spacing is one of the better solutions to overcome the said stresses. Rigid pavements are usually exposed to solar radiation severely and this incorporates with the development of varying thermal stresses as well. Rate of receiving heat flux from solar radiation, thermal properties of concrete and heat loss from concrete due to convection parameters of surrounding are the main influences of the temperature variation of an exposed concrete slab. This research produces a methodology to incorporate the temperature variation of concrete slab by the use of a 3D finite element model (FEM) approach, to estimate the relevant deformation of concrete due to its exposure to the solar radiation. ANSYS (Version 12.0.1) was used for this FEM analysis, to obtain thermal variations of an exposed pavement slab. Laboratory scale slab was used to verify the results obtained from the FEM. Verified FEM is capable of producing the lateral stresses and its corresponding deformations of concrete pavement for daily thermal variation. Lateral deformations due to shrinkage effect were calculated according to the BS 8110 part 2:1985 shrinkage model. Opening of the joint crack is restricted by the load transfer requirement in consecutive pavement slabs. Aggregate interlocking is an efficient load transfer mechanism for the thin concrete pavements which are commonly used in rural roads. Effectiveness of aggregate interlocking mechanism depends on strength of the concrete, strength of aggregate, maximum aggregate size, friction of cracked surfaces, slab thickness and joint opening. Lateral joint opening vary with the pavement life and it is directly affected to the Load Transfer Efficiency (LTE). Another key aspect of this study is to carry out an experimental investigation to obtain a relationship between crack width and LTE in a rigid pavement joints. 150 mm thick test concrete pavement slab was cast with grade 25 concrete, 20 mm coarse aggregate was used to obtain the LTE at cracked joint. Standard single axel, single wheel load of 40 kN was used to simulate the tire load. From the obtained results, it was observed that LTE decreases nonlinearly with the increase of crack width. This paper describes a procedure to obtain the joint spacing for thin rigid pavements by the use of the FEM results and LTE experiment outcome. According to the study, joint spacing for rigid pavements in rural areas can be provided even beyond the specified values of ACPA.
item: Conference-Full-text
Design of roller compacted concrete mixes for road pavements
(2001) Ekneligoda, TC; Nanayakkara, SMA
This paper presents some guidelines to carry out mix design for Roller Compacted Concrete (RCC). In order to propose a mix design method for RCC, an experimental investigation was carried out to study the properties of RCC such as wet density and flexural strength under different cement contents. A new test method was proposed to measure the wet density of RCC considering the action of a vibrating roller. The test results of wet density show that the behaviour of RCC is similar to soil with respect to optimum density. And also it was found that the flexural strength depends not only on the water cement ratio but also on the cement content. An approximate relationship was obtained for the flexural strength combining the water cement ratio and cement content.
item: Conference-Abstract
Deterioration of concrete due to delayed ettringite formation
(2013-12-06) Nanayakkara, SMA
Delayed ettringite formation (DEF) is also referred to as “Heat Induced Internal Sulfate Attack” which is an internal swelling reaction of the concrete that occurs in the presence of water without any external ingress of sulphate. Often DEF is associated with other deterioration mechanisms such as aggregate silica reaction (ASR). Crack pattern due to both DEF and ASR are very similar and therefore it is difficult to identify the exact cause for cracking without carrying out petrographic and SEM studies of the affected concrete. Cracking due to DEF was originally reported in steam-cured concrete railway sleepers but it can also occur in large concrete pours where core temperature can be very high as a result of heat of hydration. Recently, severe cracking in some of the pile caps of bridge piers in the Southern Highway project was reported. After extensive investigations, it was found that the main cause for cracking in those pile caps was DEF. It is widely accepted that concrete subjected to high temperature (>70 °C) at early age and exposed to moisture continuously or intermittently after concrete has hardened is likely to crack due to DEF. Therefore this problem can occur in thick concrete members like pile caps, deep beams, bridge piers and raft foundations. One suggested mechanism of cracking due to DEF is known as “Uniform Paste Expansion Theory”. According to this theory, expansion is taking place uniformly and isotropically in the paste phase due to conversion of monosulphate uniformly distributed in paste phase to Ettringite. The other predominant theory with respect to DEF is “Ettringite Crystal Growth Theory”. According to this theory, expansion is attributed due to pressure exerted by the growing ettringite crystals in the micro cracks between cement paste and aggregate. Since there is evidence to support both theories, both mechanisms may be possible and depending on the environmental condition one may be more prevalent. There are many factors influencing DEF and most of the time, limiting value of one factor depends on other factors. Despite extensive investigations in connection with DEF, the direct cause of damage, the chronological development of the concrete damaging mechanism, and the role of different influences such as alkali content, SO3, MgO and C3A were not yet clearly solved. However, with the present knowledge, there is a general agreement by all researchers that there is a very low risk of concrete deterioration due to DEF if the early age concrete temperature is kept below 70 °C. Apart from controlling maximum temperature rise in concrete and composition of cement, use of fly ash or slag blended cement is also effective in mitigating cracking due to DEF.
item: Conference-Full-text
Determination of tensile strain capacity of fresh concrete
(Department of Civil Engineering, University of Moratuwa, 2015-10) Weerasinghe, TGPL; Nanayakkara, SMA; Hettiarachchi, MTP
Measuring physical properties of fresh concrete is important to understand the behavior of the early phase of concrete. The measurement of tensile strain capacity of fresh concrete predicts the risk of cracking due to restrained shrinkage. Fresh concrete means the concrete before the hardening phase which is still in a semi liquid state. i.e. from right after mixing of concrete to 3 – 4 hours. Several research studies have been conducted but complex test methods have been developed to measure both stress and strain and the average strain was measured. The paper contains the procedure adopted to develop a simple test method to measure the local strain along a sample. After verifying the test method, influence of cement type for early age tensile strain capacity was studied. Ordinary Portland Cement, Fly ash blended and Portland Limestone Cement were used. Concrete was mixed as a large quantity and kept inside the mixer and agitated every 10 minutes before being taken out for testing. The method simulates the conditions where concrete is produced and kept inside a truck mixer for a while before placing. Results indicate that fly ash blended concrete has a higher tensile strain capacity than other cement types thus the mix is less vulnerable for early age cracking. Further tests should be done to determine the influence of cement type for tensile strain capacity of undisturbed concrete.
item: Conference-Full-text
Determination of Tensile Strain Capacity of Fresh Concrete: A new test method
(2016-01-06) Weerasinghe, TGPL; Nanayakkara, SMA
Measuring physical properties of fresh concrete is important to understand the behaviour of the early state of concrete. Plastic shrinkage occurs at the very early stage due to evaporation of water from the concrete surface. When concrete is restrained against plastic shrinkage, tensile strain is developed and when it exceeds the tensile strain capacity, cracks occur. This phenomenon is called as plastic shrinkage cracking. In order to assess the risk of plastic shrinkage cracking tensile strain capacity of fresh concrete should be measured. Fresh concrete means the concrete before the initial setting time which is still in a semi liquid state. The paper presents a test method developed to measure the strain distribution along a fresh concrete sample. Based on this test method tensile strain capacity of a selected mix proportion with three different types of cements, i.e., Ordinary Portland Cement, Fly ash blended and Portland Limestone Cement were determined. Results indicate that concrete with fly ash blended cement has a higher tensile strain capacity than other two cement types.
item: Article-Abstract
Development of an economical high early strength concrete mix for paving of provincial roads in Sri Lanka
Mampearachchi, WK; Kosgolla, JV; Nanayakkara, SMA
Rigid pavement construction has a long history. Readymixed or site mixed concrete is used for rigid pavement construction. However, conventional concrete mixtures require more than 7 days to gain adequate strength to allow for traffic. Development of high early strength concrete would be a solution to allow traffic within a reasonable time. However, use of high cement content in early strength concrete induces distress in the pavements and would not be an economical mix. A high performance concrete mix was developed for rigid pavement construction using a low cost admixture with available materials in Sri Lanka. Study has shown that 3% of commercial grade CaCl2 can be used as an accelerator to obtain required compressive strength and the flexural strength of concrete in 12 hours. Strength gain was verified by the maturity test conducted for a slab placed under field condition. Slab temperature was also measured with time and found temperature rise due to heat of hydration was insignificant. Using the mix proportion developed, concrete roads can be allowed for traffic in 12 hours and can also be used for repair works of the existing roads. Life cycle cost analysis was performed taking into account the construction cost, maintenance cost and the user cost. The study has shown that there is 26% saving by using high early strength concrete developed in this study.
item: Conference-Abstract
Development of dry plaster mix with manufactured sand
(2019) Vipushnan, R; Dasanayaka, DMDT; Nanayakkara, SMA
Demand for sand has increased at present due to the rapid infrastructure development in the country. As a result of excessive extraction, natural river sand has been depleted in river basins around the country. Shortage of natural sand is a current issue in the construction industry. Therefore alternatives are used for the natural river sand. Manufactured sand (M sand) has been widely accepted as a suitable alternative for natural river sand in concrete. However, M sand is not widely used for plastering and other masonry work because of the workability issues. Therefore, this research was focused on the development of dry plaster mix with manufactured sand. Dry plaster mix could contribute significantly to increase the efficiency of construction by reducing time and wastage. In this research, performance of manufactured sand in plastering mortar and the workability properties of the mortar were evaluated in order to develop a dry plaster mix. Flow table test and the Cone penetration test were used to measure the workability of mortar. The workability is low in manufactured sand mortar compared to river sand mortar. The shear resistance is high in M sand mortar compared with river sand mortar. Therefore air entraining additives were introduced to reduce the shear resistance. Results show that the shear resistance increases about 50% from its initial value in both river sand mortar and manufactured sand mortar in two hours. Also it was observed that the workability loss is rapid when air entraining agents are present. Addition of lime improves the workability of manufactured sand mortar similar to that of river sand mortar. Results show that Cement: Lime: Sand mix ratio of 6: 2: 30 as optimum for a lime based manufactured sand dry plaster mix in order to match the workability of the same cement: sand ratio mortar mixture with river sand. Addition of lime allows retention of workability of manufactured sand mortar with time. Raw material cost is lower for lime based manufactured sand plaster compared to the river sand plaster mix.
item: Conference-Abstract
Development of fibre reinforced paving block for outdoor sports surfaces
(Department of Civil Engineering, 2023-09-27) Gannoruwa, GKBM; Muthurathne, SSK; Nanayakkara, SMA; Mallikarachchi, C; Hettiarachchi, P; Herath, S; Fernando, L
Synthetic fibre blended fabric offcuts generated from textile industry are considered as waste and currently incinerated in cement kilns. Utilisation of textile waste in development of cement based product was focused in this study. Behaviour of fabric pieces in cement matrix indicates its reinforcing effect with proper bonding characteristics while changing its failure pattern from brittle mode to more ductile pattern. Experimental investigation was carried out to identify the optimum size of shredded fabric pieces and its content which can be incorporated into cement matrix to achieve the highest flexural strength of the fabric-cement composite. Optimum fabric content was found to be 26% by volume and most suitable size range of shredded fabric pieces was identified as 0 to 10 mm. Superplasticiser was used to improve the workability of mixture at low w/c ratios and viscosity modifier was used to improve the homogeneity. Paving block was developed with the use of shredded form of polyester spandex fabric, manufactured sand, cement and admixtures. Developed block complies with the requirements specified for paving blocks in SLS 1425 and BS EN 1338 standards. Fiber reinforced paving block has a compressive strength of 18 MPa and tensile splitting strength of 5.4 MPa. Under compression type load, the block is initially subjected to elastic deformation and then plastic deformation. Failure pattern changing point from elastic deformation region to plastic deformation region was considered as failure point of that block to estimate its compressive strength. The developed paving block has an abrasion resistance of 17 mm and a skid resistance of 80 USRV. Elasticity effect of polyester spandex fabric leads to improve the shock absorption characteristics of fibre reinforced paving block. The shock absorption capability of this paving block was measured using a test apparatus that was fabricated in accordance with the BS EN 14808 standard, which specifies the determination of shock absorption characteristics of sports surfaces. The shock absorption capability of this block is 21%, which meets the requirement specified in the BS EN 15330-1 standard for tennis court surfaces. Incorporation of fabric pieces into cement matrix leads to create a porous structure while improving water infiltration capability. Permeability of the paving block was measured in terms of its infiltrated water volume at constant time intervals under constant pressure head. This paving block has a water percolation capability of 200 litres/m2 per hour, which means it can absorb up to 100 litres of water per square meter in 30 minutes under a pressure head of 1.1 bar. This helps to reduce surface runoff of rainwater. Deterioration of fabric fibres in an alkaline environment was evaluated as per ISO 8336 standard while subjecting fibre reinforced paving blocks to 50 numbers of soak–dry cycles and soak-dry performance criteria was estimated as 0.8 which satisfies the ISO 8336 standard requirement. Developed paving block satisfies the requirements specified for paving blocks in SLS and BS EN standards. The novel paving block has improved shock absorption and water infiltration characteristics, as well as satisfactory durability. It is suitable for outdoor sports surfaces, as it provides better foot comfort and slip resistance.
item: Conference-Extended-Abstract
Development of fly ash based geopolymer concrete
(2011) Silva, SVA; Kithalawa Arachchi, JNJ; Wijewardena, CL; Nanayakkara, SMA
This paper describes the research carried out to develop a geopolymer concrete based on alkali activated Fly Ash by Sodium Hydroxide with Sodium Silicate . Tests were carried out to investigate the properties of geopolymer paste, mortar and concrete varying different parameters to obtain optimum mix proportion. Higher values of compressive strength was recorded for all three forms compared to Ordinaty Portland Cement concrete within a lesser time period and results indicated that the higher water content within all three forms had an adverse impact on the compressive strength. Even with these advantages the main drawback was the curing method and the curing time which was essential for the polymerization process and it was found out that only half of the compressive strength of the heat cured sample urn achievable when it was kept under room temperature for 28 days. Most of the results were very promising and showed a great potential for this material as a substitute for Ordinaty Portland Cement concrete.