Prediction of the lifespan of cement at a specific depth based on the coupling of geomechanical and geochemical processes for CO2 storage

The injection of carbon dioxide (CO2) captured from combustion-based processes into underground formations is one of a number of plausible methods to reduce its release into the atmosphere and consequential greenhouse gas warming. Once the gas has been captured efficiently and effectively, depleted oil and gas reservoirs are seen as high potential candidates for carbon storage projects. However, legacy issues associated with a high number of oil and gas wells abandoned during the last few decades put the carbon capture and storage projects (CCS) at risk. These include any defects within the cement surrounding the well casing or for capping an abandoned well that can become unwanted CO2 leakage pathways. To predict the lifespan of these cements due to exposure to CO2-bearing fluids at the conditions found underground, the geochemical processes need to be coupled with the geomechanical changes within the cement matrix. In a viable CCS project for sequestering CO2, the cement matrix should be capable of withstanding acidic environments formed by dissolution of CO2 in brine for more than ten thousand years. This work aims at providing a framework to predict the behaviour of cement due to CO2 exposure under reservoir conditions. The results show that the chemical reactions and geomechanical changes within the cement matrix can result either in its radial cracking or radial compaction. Both of these behaviours are investigated as possible phenomena which may affect the CO2 leakage, and therefore the viability of the site for long term carbon storage

Utilization of Poly(Polyvinyl Alcohol-g-2-Ethylhexyl Acrylate) as Admixture for Mortar

We investigated the physico-mechanical properties of mortar mixed with copolymers based on polyvinyl alcohol (PVA) and 2-ethylhexyl acrylate (2-EHA) and synthesized by grafting using ammonium persulfate (APS) as an initiator. Increasing the amount of 2-EHA in the copolymer from 4% to 8% reduced the water/cement (W/C) ratio, the initial and final setting times, and the water absorption of mortar, while it increased its compressive strength.<br/

Comparing flexural behaviour of fibre-cement composites reinforced bagasse:wheat and eucalyptus

In this paper the applications of Agricultural Waste Fibres (AWF) are considered in producing the Fibre Cement Boards (FCB). Three different AWFs including bagasse, wheat and eucalyptus fibres as 2% and 4% by the weight of Portland cement, were used to produce FCB. Moreover, the effect of silica fume on flexural behaviour characteristics of FCB has been studied. The results show that the flexural behaviour of the FCBs depends on the type, length, diameter, aspect ratio and texture of fibres. Also for all groups with increasing fibre content from 2% to 4% of cement weight, maximum flexural strength increases. Moreover, silica fume could improve the flexural strength for all the groups

Gypsum: prospects for recycling

The term gypsum is used to refer to three main compounds of calcium sulphate: anhydrite, hemihydrate and dihydrate; but it is most often used for the dihydrate. The two main industrial uses of these compounds are in cement and in plaster products. Cement producers use a blend of gypsum and anhydrite as a set controller. Plaster is made with hemihydrate. This material is used both for bagged plaster and also to feed the plasterboard production lines. The materials are available from both primary and secondary sources.Waste plasterboard is an increasingly important secondary source but there are a number of problems which limit the proportion of thismaterial that can be used in plasterboard production. Research is therefore in progress to find other uses for it, such as lowstrength concrete mixes

The effect of Persian Gulf tidal zone exposure on durability of mixes containing silica fume and blast furnace slag

In this research the performance of cement paste and concrete mixes incorporating 7% and 10% of silica fume (SF) as a cement replacement was investigated in three exposure conditions. The results showed that plain type II portland cement performed better than blended SF cement under cyclic wetting and drying conditions. Silica fume specimens under cyclic wetting and drying conditions in simulated seawater exhibited higher strength loss compared to plain type II portland cement where cured under potable water. In addition, the greater the silica fume amount used in the mixes, the more the capillary water absorption under tidal zone exposure or/and under wetting and drying simulation. Further, the ternary blended ground granulated blast furnace slag (GGBS) mix was the worst performing mix in all exposure conditions

Distribution pattern of phytoplankton (Chrysophyta and Pyrrophyta) in the southern Caspian Sea

In regard to study the distribution pattern of phytoplanktons (with emphasize on chrysophyta and pyrrophyta), a series of 4 cruises were carried out seasonlly in 1996. A total of 93 species belong to 2 main phyllums of chrysophyta (mainly diatoms) and pyrrophyta were identified consist of73 and 20 species, respectively. The diatoms have an important role in the whole Caspian Sea from point of species diversity and on the other hand contain the most abundance and biomass in all seasons. There are two main species of Rhizosolenia calcaravis (belong to chrysophyta) and Exuviealla cordata (from Pyrrophyta) inhabit in the southern Caspian Sea. Comparing the density and biomass of different phyllums of phytoplanktons showed that chrysophyta with 75% and pyrrophyta with 17% are the most abundant phytoplanktons in the said region

Nonconventional Ca(OH) ₂ treatment of bamboo for the reinforcement of cement composites

This study compares the structural and morphological changes in Guadua angustifolia Kunth (GAK) fiber prepared in three different ways (chips, barkless and crushed) when non-conventional alkaline treatment is applied. Moreover, it shows the improvement of mechanical properties of cement composites reinforced with these treated fibers. The three different preparations of Guadua were treated with a saturated solution of calcium hydroxide (5%) at 125 &deg;C and 1.25 kPa for 3 h to remove non-cellulosic compounds. Then, their chemical, morphological, and structural properties were examined. The fibers exhibiting the higher delignification rate were selected to prepare cement composite boards, whose mechanical properties were successively compared with those of composites reinforced with untreated G. angustifolia fibers. The water/cement ratios of the cement mixed with the Ca(OH)2-treated and the untreated fibers were, respectively, around 0.3 and 0.25. The flexural strength and toughness of the two composites were evaluated after 7, 28, and 90 days of curing. The calcium hydroxide treatment showed higher efficiency in removing non-cellulosic materials when performed on crushed bamboo; moreover, the mechanical properties of the composites reinforced with the treated fibers were higher than those mixed with the untreated ones. After 90 days of curing, the flexural strength increased by around 40% and the toughness became three times higher (p &lt; 0.05). The mechanical improvement by the Ca(OH)2 treatment of G. angustifolia fibers demonstrates its potential for the fabrication of cement composites