The durability of cement paste is one of the most topical field nowadays that economic restraint and conservation will remain the rule of the day. The term "degradation" means that the cement paste fails to serve the intended purpose for the length of time expected. It should be noted that normally, cement paste often does have an essentially indefinite life span, in the absence of degradation processes [32]. Physico-chemical cement degradation can be thought of in two categories. They are physical action which breaks hardened cements down into smaller fragments and chemical action which alters their components into different species and chemical action usually consisting of dissolution of matter and formation of a new phase [45]. Among mechanism of cement paste degradation due to chemical and physical factors are alkali-silica reaction, sulphate attack, chloride reaction, carbonation, leaching, and freezing and thawing [45]. Example of chemical degradation process can be observed in alkali-aggregate reactions such as dissolution of silica and the formation of silica gel. This reaction involves breakage of bonds between the aggregate and the paste [32]. An example of physical degradation process is the reaction of Ca(OH)2 and C-S-H with CO2 causes carbonation shrinkage. It may lead to the loss of structural integrity such as volume instability, cracking and loss of strength [32]. Laboratory experiments have shown that cement degrades would occur once exposed to such CO2 rich environments [10]-[12], [16], [22], [72]-[74], [30]. It tends to degrade rapidly once exposed to such acid gas by reacting with Ca(OH)2 and C-S-H. The mechanism of degradation process starts when CO2 gas is exposed in a wet environment, it will... ... middle of paper ... ...3 occured by an acid attack after a complete removal of Ca(OH)2 at low pH as shown in Equation 2.10. CaCO3 + H2CO3 → Ca(HCO3)2 (2.10) In these reactions, CaCO3 is converted to water soluble calcium bicarbonate (Ca(HCO3)2) which can then react with Ca(OH)2 to form CaCO3 and additional water as shown in Equation 2.11. Ca(HCO3)2 is two orders of magnitude more soluble than Ca(OH)2 [33]. As such, the water produced in Equation 2.11 will dissolve more Ca(HCO3)2. As the leaching of this material continues from the cement matrix, dramatic increases in porosity and permeability would occur. Ca(HCO3)2 + Ca(OH)2 → 2CaCO3 + H2O (2.11) In addition, the additional water produced from each reaction may allow production of H2CO3 when react with CO2 as in Equation 2.4 and thus a continuation carbonation process might occur.
Hydrochloric acid + calcium carbonate arrow calcium chloride + carbon dioxide + water. HCl(aq) + CaCO3(s) arrow CaCl2(aq) + CO2(g) + H2O(l) Things that affect the reaction rate of this experiment are: 1. The temperature of the hydrochloric acid. 2.
(Mazzassa – Lea's science). Calcium silicate hydrate is the fundamental result of lime-pozzolan response. Calcium aluminous hydrate, hydrated gehlenite, calcium carboaluminate, ettringite and calcium aluminous monosulfate are a percentage of alternate items that outcome from the lime-pozzolan response notwithstanding calcium silicate hydrate. (Admixtures for cement T.erdogan). The hydration between slica of pozzolans and calcium hydroxide are given by mathematical statement.
Investigate how the concentration of hydrochloric acid effects the rate at which it reacts with calcium carbonate
Aitcin P.C, “Cements of yesterday and today Concrete of tomorrow”, Cement and Concrete Research, Vol. 30, (2000), pp 1349 - 1359.
Presently Portland cement and supplementary cementitious materials are cheapest binders which maintain/ enhance the performance of concrete. However, out of these binders, production of Portland cement is very energy exhaustive
The ability of a hardened cement paste retain its volume after setting without delayed destructive expansion
...07). Report 38: Durability of Self-Compacting Concrete - State-of-the-Art Report of RILEM Technical Committee. Bagneux: RILEM Publications.
Water : Water is an important ingredient of concrete as it actually participates in the chemical reaction with cement. Since it helps to from the strength giving cement gel, the quantity and quality of water are required to be looked into very carefully.
The proto type performed satisfactorily with regard to drying and hardening shrinkage, heat of hydration, denseness after hardening, and other properties. This concrete was named “High Performance Concrete” and was defined as follows at the three stages of concrete:
Concrete is a composite material composed of water, coarse granular material embedded in hard matrix of material (the cement or binder) that fills the space among the particles and glues them together. Concrete is known by Romans as old as 12 million years. It was a revolutionary material laid in the shape of arches, vaults and domes. Concrete is widely used for making architectural structures, foundations, brick/block walls, pavements, bridges/overpasses, highways, runways, parking structures, dams, pools/reservoirs, pipes, footings for gates, fences and poles and even boats. From roman to now Concrete has taken many designs. Present researchers have experimented with addition of materials to create improved properties such as strength or electrical conductivity.
These cement stabilised material are characterized by its stiffness property and its tensile strength. AUSTROADS (2008), NCHRP (2004) recommends Mechanistic-Empirical (M-E) approach in which material is characterized by its resilient stiffness modulus and thickness design by cumulative damage analysis using fatigue life analysi...
Valeria Corinaldesi, et al. evaluated compressive strength of concrete. The Compressive strength of concrete was determined at 3, 7 and 28 days age of curing. The addition of both red and blue pigments caused a certain strength loss never higher than 3 MPa. Moreover, the use of CaO together with shrinkage reducing admixture (SRA) allowed to fully recovering the slight strength loss due to the red pigment addition. At the dosage of 20 kg/m³ slightly reduces concrete compressive strength. The use of shrinkage reducing admixture and CaO proves to be very effective in reducing the risk of concrete cracking and it also gives positive contribution on concrete compressive strength
Ghani et al (2006), determined the effect of temperature on different properties of concrete using different mix ratios of 1:1:2, 1:1.5:3, and 1:2:4, and water-cement ratios of 0.35, 0.40, 0.45, 0.50, 0.55, and 0.60, for cubes, cylinder sand beams. The concrete produce were cured in different room temperatures of 5oc, 55oc, and 28oc.Based on theirs, the following assertions were made.
Aggregates those are chemically inert materials which when bonded by cement paste to form concrete constitute the bulk of total volume of concrete & hence they influence the strength of concrete to a great extent. Depending upon their size, the aggregate are classified as the fine aggregate & coarse aggregates. The material passing through 4.75 mm sieve size is termed as fine aggregates. Natural sand or crushed sand is usually mainly as fine aggregates in concrete mixes.
Strength is an important property for restorative materials, which depends on the microstructure and composition of material, the method of testing the fracture mechanism and the environment (20). The measurement of compressive and flexural strength is one of the methods to investigate the mechanical properties of restorations (21). Flexural strength is one of important characteristics of MTA. This property becomes more important when the MTA is placed under occlusive pressures, such as when MTA is used as pulpotomy material or direct pulp coating or forcal perforation repair. In such cases, the flexural strength of the MTA should be greater than the strength of the amalgam condensation to prevent the fracture of the MTA. Considering the clinical applications of MTA and other suitable materials in perforation repair, the bonding strength of these materials is an important factor in providing a suitable and optimum seal between the root canal system and the material.