Alkali-aggregate Expansion Research Articles

A Study on the Mechanical Properties of Alkali Activated Concrete Using Various Types of Synthetic Zeolites

Abstract -The world's most common man-made material is concrete. Portland cement is a key component of a typical concrete mix. However, about 5% of the world's carbon dioxide emissions are brought on by the manufacture of cement. Engineers and scientists need to invent and use a green building material to make the world more sustainable. Due to its corrosion resistance, geopolymer concrete is also significantly more durable than regular concrete. It is also significantly stronger than regular concrete. The development of green construction will be facilitated by the innovative sustainable building material known as geopolymer concrete. Alkali- activated materials also known as geopolymers, are made from a variety of materials (usually industrial byproducts) known as precursors. These are combined with an alkaline medium to create a cementitious material that can be used in place of Portland cement in the production of concrete. Mineral admixtures (such as fly ash and GGBS) are typically added in larger amounts in concrete to improve its workability, resistance to thermal cracking, alkali-aggregate expansion, and sulphate attack, and to allow for a reduction in cement content. In the current study, sodium hydroxide and sodium silicate were used as alkaline activators with a Molarity of 12M, and fly ash, GGBS, and types of synthetic zeolites as binder ingredients. 40% of GGBS is kept constant and fly ash is replaced with zeolite in various percentages. In this paper, zeolite is replaced with 5%, 7.5%, and 10% of fly ash to create geopolymer concretes. Zeolite powder obtained by the calcination process with the aid of sodium hydroxide and fly ash, industrial wastages. The performance of the created concrete is then evaluated using mechanical behavior on developed mix. Key Words: Alkali activator, fly ash, Ground granulated blast- frunace slag, synthetic zeolites, strength properties.

Study on Analysis Method and Control Index for Deformation of Super-High Arch Dam Suffering Alkali-Aggregate Reaction

Alkali-aggregate reaction can not only cause uneven expansion of concrete but also lead to cracking and even destruction and consequently affect the working behavior and long-term safety of hydraulic concrete structures. Present researches on alkali-aggregate reaction focus on improving the composition ratio of concrete materials through experimental study to inhibit the reaction, whereas there is a lack of quantitative calculation and analysis. In the present study, the problem of alkali-aggregate reaction in the super-high arch dam of Jinping I Hydropower Station was taken as an example. The expansion of concrete suffering the alkali-aggregate reaction was simulated by means of the overall temperature rise in the dam. Similarly, the yield zone, the expansion process, and the deformation change law with the development of concrete expansive deformation under various load combinations were analyzed by using the elastic–plastic finite element method. Finally, a control index of allowable alkali-aggregate expansion of dam concrete under various load combinations was put forward. The research results demonstrated that the control index was 400~800 με. Since the arch dam has a low safety reserve when operating at a low water level, the lowest reservoir level should be raised as much as possible in dam operation to reduce its drawdown rate, thus restraining the adverse impact of alkali-aggregate reaction in concrete on the dam.

Influence of composite materials confinement on alkali-aggregate mechanical behaviour

In a previous study [6], we have presented an original experimental procedure for results expansion alcali aggregate reaction. Our main goal is to identify the influence of the confinement by composite materials on alkali-aggregate expansion.

Influence of composite materials confinement on alkali aggregate expansion

Influence of composite materials confinement on alkali aggregate expansion

Influence of composite materials confinement on alkali aggregate expansion

The Alkali-Aggregate Reaction (AAR) is a group of physicochemical reactions which occurs in the concrete between the interstitial solution (highly alkaline) and some mineral phases in the aggregates. The damage induced by the AAR to the concrete could be very important. Many old structures are attacked or will be attacked by AAR. Remedial measures to repair or limit the problem exist but they are often only partially effective and very expensive. The aim of our research is to carry out an experimental procedure in order to evaluate the influence of advanced composite materials confinement on the expansion and the mechanical behaviour of the alkali-aggregate reactive concrete.

Restrained alkali–aggregate expansion due to steel fibre additions in concrete

The work reported here shows that steel fibres can reduce the expansion caused by alkali–aggregate reaction in concrete, hereby decreasing the resulting strength loss. The addition of 1–1·5% of steel fibres by volume allowed us to increase the alkali content by about 2 kg/m3. Under such conditions, the ultrasonic pulse velocity was found to be stable, and the expansion rate low, indicating only minor effects on the strength of the concrete, even though the concrete contained reactive aggregate and a high alkali content. More specifically, the effliciency of fibres for restricting expansion is governed by the size and geometric parameters of the fibres. The expansion rate was linearly related to the so-called fibre factor or fibre index, for otherwise similar alkali–aggregate reaction conditions.

Influence of Dimension of Test Specimen on Alkali- Aggregate Reactive Expansion

The influence of the dimension of the test specimen on the expansion of both alkali-silica reaction (ASR) and alkali-carbonate reaction (ACR) is studied. The results show that the dimension of the test specimen markedly influences ASR expansion, but not ACR expansion. For ASR expansion, the larger the aggregate, the greater the influence of the test specimen dimension. From two processes of the transference of heat and the transference of mass, the reason that test specimen dimension influences alkali-aggregate reactive expansion is analyzed. The loss of the activated compound in the aggregate is considered an important reason.

Alkali-aggregate expansion inhibiting admixtures

Many concrete structures have exhibited deterioration due to the alkali-aggregate expansion reactions. A review has been prepared to describe the nature of the alkali-aggregate reactions, test methods that are adopted to evaluate the aggregates for their potential to cause expansion and the methods suggested to counter this reaction. Some methods seem to be effective but further work has to be carried out before establishing the efficacy of others. Results obtained using additives such as silica fume and other siliceous materials such as fly ash, slag, and rice husk ash have been discussed. Some chemicals based on lithium compounds have shown promise as, also, have other non-lithium bearing compounds.

亜硝酸リチウムによるアルカリ骨材膨張の抑制効果

The effect of LiNO2 on the suppression of expansion due to alkali-aggregate reactions was investigated by preparing mortars with a reactive andesite sand and measuring the expansion at the prescribed times of the mortars cured up to 7 months. The test results showed that the addition of LiNO2 giving a Li/Na mole ratio of 0.4 conspicuously suppressed expansion of mortars stored in a fog box and immersed in 1N NaCl solution at 40°C. Furthermore, none of the mortar specimens containing the amount of LiNO2 which exceeded a Li/Na mole ratio of 0.8 expanded even under the severe condition of 6 months immersion in 1N NaOH solution at 20°C. Expansion tests of mortars using reactive sand particles impregnated with LiNO2 solution were conducted as well. The use of the impregnated sand particles was found to suppress expansive alkali-aggregate reactions promoted by the intrusion of Na+, Cl-, and OH- ions. it was also confirmed that the compressive and tensile strengths of mortars changed little by the application of LiNO2. The results obtained show that LiNO2 may be able to use as a chemical admixture for preventing alkali-aggregate expansion of concrete.

Alkali aggregate reactivity in dense concretes containing synthetic or porous natural aggregate

Studies have been made into the relative importance of pore solution dilution, accomodation of gel pressures and potential reactivity of porous aggregate in the suppression of alkali aggregate expansion in concretes containing a pessimum proportion of Thames Valley sand. The results also indicate that the alkalinity of the pore solution may be more direct measure of susceptibility to reaction than the Na 2O equivalent content of the concrete. Slow reactivity in some sintered aggregates has been monitored for up to 10 years and the relatively low expansions are discussed in terms of fluxing impurities in the glassy phases.

Portland-zeolite-cement for minimizing alkali-aggregate expansion

The Authors give an account of the performance modifications induced in the blended cements by replacing the typical pozzolanas with their zeolitic counterparts: volcanic tuffs, after suitable grinding. The advantages of such a replacement in terms of minimization of alkali aggregate expansion and of strengths increase long ages are discussed, emphasizing also the favourable influence of expansion abatement supplied by a previous thermal treatment of the zeolitic addition. The improved strength progress is interpretated in terms of a higher reactivity of the zeolite minerals in comparison with that of the pozzolanic glass and the expansion abatement in terms of ability to incorporate high alkali amounts showed by the abudant amorphous hydrated sil i cate.

Mechanism of Pozzolanic Reactions and Control of Alkali-Aggregate Expansion

Abstract The mechanism of pozzolanic reactions and their control of expansion caused by alkali-aggregate reaction was investigated. Mixtures of tricalcium silicate, opal, sodium hydroxide, and water having calcium oxide to silica mole ratios from 1.07 to 3.0 were prepared and reacted from seven days to four years before filtering. The solids (precipitates) were studied by X-ray diffraction to determine the phases present, and the alkali content of filtrates was obtained by chemical analysis. Results suggest that pozzolans reduce or eliminate alkali-aggregate expansion by producing additional calcium silicate hydrate and low lime calcium silicate hydrate. These hydrates can retain additional alkali, thus reducing the amount of alkali available for reaction with reactive aggregate. In order to control alkali-aggregate expansion by the addition of pozzolan, such as fly ash, results indicate that about 30% low lime fly ash is required. However, this amount could be reduced considerably, to a level as low as 20% (cement basis), if the concrete contains reactive siliceous aggregate.

Performance of Blast-Furnace Slag Cement

Abstract The sulfate resisting portland cement is obtained from a special portland cement clinker with low-tricalcium-aluminate content. In Western Europe another cement is used more for constructions in sulfate environments than portland low-tricalcium-aluminate cement, the blast furnace slag cement with slag content higher than 70%. According to ASTM standard Specification for Concrete Aggregates (C 33), when reactive alkali-aggregates are used, portland low-alkali cement is recommended. According to the European experience, the blast-furnace slag cement with slag content greater than 70% does not produce any expansion when used with stone materials of potential alkaline reactivity. This paper deals with the performances of blastfurnace slag cements tested for sulfate resistance and for alkali-aggregates reaction. The results obtained fully confirm the possibility of overcoming the risk of alkali-aggregate expansion and sulfate destruction by using blast furnace slag cements with high-slag content. The lower energy cost of blast-furnace slag cement, which can replace the special portland cement with low-tricalcium aluminate and low-alkali content, may favor its use.

Effect of phlogopite mica on alkali-aggregate expansion in concrete

The tensile strength of concrete is increased by the addition of high aspect-ratio mica reinforcement. Phlogopite mica contains about 10% K 2O; soluble K + would contribute to the alkalinity of the pore solution in concrete enhancing its potential expansivity if it is made with alkali-expansive aggregate. Electron microprobe analysis confirms that the solubility of K + from phlogopite in cement paste, about 0.09% is the same as in mixed calcium-sodium-hydroxide solutions. The addition of 1.5% by volume of phlogopite to concrete prisms made with alkali-carbonate expansive aggregates caused a small increase in the rate of expansion of prisms made with both high and low alkali cement. It is concluded that the addition of small quantities of phlogopite as a reinforcement in concrete is not a cause for concern, although caution should be exercised in adding larger volumes to concrete made with potentially alkali-expensive aggregate.

New Approach to Inhibiting Alkali-Aggregate Expansion

First Name is required invalid characters Last Name is required invalid characters Email Address is required Invalid Email Address Invalid Email Address

Alkali-Aggregate Expansion Corrected with Portland-Slag Cement

First Name is required invalid characters Last Name is required invalid characters Email Address is required Invalid Email Address Invalid Email Address