Papers by Keyword: Drying Shrinkage

Abstract: In reinforced concrete structures constructed on the coastline of the hypersaline Arabian Gulf water, corrosion of reinforcing steel causes cracking, delamination and spalling of concrete, within a time span of a few years. The King Abdullah Civic Center (KACC), being constructed on a reclaimed land off the coastline in the Eastern region of Saudi Arabia, is a major complex with wharves, quay walls, and breakwater and commercial buildings. To ensure the durability of buildings in the harsh marine environment and to provide a minimum service life of 35 years, a concrete mix in which 70% of Portland cement is replaced by granulated ground blast furnace slag (GGBFS) was recommended based on durability modeling conducted using the software STADIUM^®. Concrete with 70% GGBFS provides for the dual objective of achieving a green concrete and an enhanced service life of the building. Based on durability modelling it was concluded that corrosion inhibitor should be used preferably in the concrete. A detailed experimental program was conducted to assess the durability and strength properties of the 70% GGBFS concrete, with and without corrosion inhibitor. This paper presents the results of experimental investigations and durability modeling conducted for the project. A 70% GGBFS concrete mix without corrosion inhibitor was adopted for the raft foundation and subsequently for the entire building to make it a green concrete building.

Abstract: The objective of this research was to quantify the effect of the mixing temperature, as well as curing conditions, on concrete mechanical and durability properties. Sixteen mixtures were cast and specimens were tested at various ages. The w/c ratio of the mixtures was kept constant, whereas the type of aggregates, casting and curing temperature varied. A concrete batch was designed using low absorptive Normal Weight Aggregates (NWA), whereas a second concrete batch included High Absorptive Normal Weight Aggregates (HANWA), at a saturated surface dried (SSD) condition. The HANWA were intended to deliver internal curing water (IC) to the mixtures in order to improve their performance. The mixtures constituent materials were conditioned at 22, 30, 35 and 40 degrees Celsius prior mixing. Two different types of curing regimes have been applied, aiming to evaluate the effect on specimens exposed to both hot environmental conditions and also day to night temperature fluctuations, as opposed on identical, water cured specimens. It was observed that the HANWA mixtures had improved mechanical and durability properties, a fact that was attributed to IC.

Abstract: The influence of magnesium to phosphate weight ratios (M/P ratio), borax content, water to cement ratio (w/c ratio), fly ash, slag on magnesium phosphate cement of drying shrinkage is examined.The results show that the drying shrinkage of magnesium phosphate cementcan be affected at some extent by M/P ratio, w/c ratio,boraxcontent. Both the former two factors and the effects are significant.It was found that the drying shrinkage of magnesium phosphate cement decrease with the increase of M/P ratio,borax content, w/c ratio. If the 10%, 15% offly ashinstead of magnesium phosphate cement was added, drying shrinkage rate decreases with increases of dosage fly ash. When the 15% of magnesium phosphate cement is replaced by fly ash, the shrinkage rate of hydration 20d reachs11.2×10^-5. When the 10% of magnesium phosphate cementis replaced by slag, the drying shrinkage rate reducedto 87.6%.comparing to the bench mark ,the drying shrinkage rate of 20d is only 2.78×10^-5.

Abstract: Influences of polypropylene (PP) fiber and hydroxyethyl methyl cellulose (M) on the shrinkage rate of cement mortar and its potential mechanism were investigated. Results show that both the addition of trilobal PP fiber and M would reduce the shrinkage rate of cement mortar if well applied. With the increasing of PP content, the shrinkage rate firstly decreases and then increases, and reaches the lowest shrinkage degree with fiber content of 0.20% (volume fraction). While for cement mortar with M, the greater the dosage, the less drying shrinkage rate. An addition of 0.6% M contributes to a decrease of 23.8% for the 180-days drying shrinkage than the control. Additionally, a combination of both PP fibers and M can significantly reduce the drying shrinkage of mortar, resulting in a decrease of 40% for the shrinkage rate.

Abstract: Drying shrinkage in mortar produces cracks and micro-cracks which affect the durability of a structure. The effects of seawater as a substitute to freshwater and fly ash as a partial replacement for cement were investigated in this study in order to address the predicted water shortage by 2025 and the increasing carbon footprint from carbon dioxide emissions worldwide. Moreover, these materials are also more economical alternatives to freshwater and cement. Rectangular prism specimens with varying fly ash content (10%, 15%, 20%, 25%, and 30%) were cast to measure the drying shrinkage in mortar while 50-mm cube mortar specimens were prepared to determine the compressive strength. This study investigated whether the addition of fly ash and seawater reduced the drying shrinkage of mortar. From the results, it was found that mortar specimens with 20% fly ash replacement achieved the highest early and late strengths. Partial substitution of fly ash would result to shrinkage in mortar while substitution of seawater to freshwater counteracts the effects of fly ash, thus producing less shrinkage. Fly ash content between 20%-25% combined with seawater produces the least shrinkage value without compromising the minimum required compressive strength.

Abstract: Aim of this work is to investigate the feasibility to implement structural mortar containing forest biomass ash (FBA), produced by a local power plant, in partial replacement of cement. Chemical composition, morphology and pozzolanicity of ash have been evaluated using Energy Dispersive X-ray analysis (EDX), SEM and Chapelle test respectively. Furthermore, fresh state properties and drying shrinkage, compressive and flexural strength of the mortars at different curing times have been investigated. Forest biomass ash at replacement levels of 0%, 10%, 20% e 30% by total binder weight has been used. FBA has been found to show only a very moderate pozzolanicity, while it adversely affect workability of the fresh mortar and compressive strength and drying shrinkage of the hardened mortar. Nevertheless, at a replacement level of 30%wt and after 28 days of curing, mortar showed a compressive strength above 30MPa.

Abstract: Capillary tention is one of the driving forces of shrinkage of cement-based materials, which is related to distribution of pore size, surface tension of pore water, contact angle of pore walls and so on. There are some appropriate test methods for pore diameter and surface tension of cement-based materials, but the contact angle of pore water is rarely related to. This paper showed a new method to test the contact angle of cement-based materials which is based on the principle of thin-layer wicking about surface physical chemistry. Combining Washburn equation x²=(Refft/2) , the contact angle of analog pore solution to cement paste was obtained. The influence of superplasticizers and mineral admixtures on the contact angle and drying shrinkage of cement pastes also were researched. The results showed that the larger contact angle leads to the smaller surface tension of pore solution, which also caused that the capillary wall wass infiltrated more difficultly. As a result, the pressure of pore and the drying shrinkage were both small, vice versa.

Abstract: In this paper, the influence of water cement ratio, prewetting degree of lightweight aggregate, flyash content and air content on the internal relative humidity (IRH) and drying shrinkage of lightweight aggregate concrete (LAC) were studied using a relative humidity sensor and drying shrinkage apparatus. Results showed that the IRH of concrete decreased rapidly at early age and slowed down at late age, and prewetting lightweight aggregate could compensate the loss of IRH. The effect of compensation could be enhanced with the increasing of prewetting degree of lightweight aggregate, and the addition of flyash retarded the decrease of IRH at early age. The drying shrinkage of LAC increased quickly at early stage and it slowed down to the even after 60 days or longer age. Furthermore, the drying shrinkage of LAC increased with increasing of water cement ratio. The effect of air content on the drying shrinkage of LAC was limited at early stage. However, at the late stage it grew at different level with increasing of air content. By raising the prewetting degree of lightweight aggregate, mixing with proper dosage of flyash, the shrinkage rate of LAC can be reduced markedly. Key words: lightweight aggregate concrete, internal relative humidity, drying shrinkage, prewetting degree, flyash.

Abstract: UltraHigh Performance Fiber Reinforced Concrete (UHPFRC) exhibits remarkable mechanical performance, which can allow to reduce the cross-section of structural members. However,a problem involving UHPFRC isthe likely tendency to crack at early age, due to autogenous and plastic shrinkages, caused by the very low water-to-binder ratio adopted. Therefore, this experimental work intends to detect the effectiveness of a possible solution for reducing the risk of shrinkage cracks in UHPFRC, by adding to the mixture a suitable combination of expansive and shrinkage reducing agents.Compressionand bending testswere carried out up to28 days of curing. Free drying shrinkage strains were evaluated up to 56 days of exposure to 50% relative humidity. The experimental results obtained by using expansive and shrinkage reducing agents were extremely encouraging in termsof free dryingshrinkage reduction, and even surprising in terms of flexural behaviour.

Abstract: –The drying shrinkage behaviour of fly-ash-based self-compacting geopolymer concrete (SCGC) was studied for a period of one year. Two SCGC and One OPC-based conventional mixture were used in the present investigation. Drying shrinkage test commenced on the 7th day after casting the test specimens. Once the appropriate curing regime was completed, the specimens from each mix were placed in the laboratory room where the temperature was maintained at 23°C, however, the relative humidity of the room varied between 56 and 64 percent. Strain readings taken at specific intervals were analyzed to determine the time-dependent deformations of each mixture. Test results indicated that the heat-cured fly ash-based SCGC experienced very low drying shrinkage than that of water-cured OPC based concrete. After one year of exposure, in comparison to 466 με, the value experienced by OPC concrete, the drying shrinkage strains of SCGC mix specimens ranged between 141 and 159 με. These values were about 65-70% lower than that of OPC concrete. It is anticipated that the findings of this investigation would help in predicting the behaviour of SCGC. Keywords-Fly ash, Geopolymer concrete, Self-compacting Geopolymer concrete, Drying shrinkage