Porosity Of Mortar Research Articles

THE INFLUENCE OF COARSE AGGREGATE CONCENTRATION ON THE STRENGTH OF CONCRETE AND ON THE POROSITY OF CONCRETE MORTAR/STAMBIOJO UŽPILDO KONCENTRACIJOS ĮTAKA BETONO STIPRUMUI IR SKIEDININĖS DALIES PORINGUMUI

The results of experiments dealing with coarse aggregate concentration influence on the concrete strength and the structure of hardened cement paste and mortar of concrete are presented in the paper. Experiments were performed on concrete with dense coarse aggregate (crushed granite) which strength is more than strength of mortar and lightweight porous aggregate (expanded clay aggregate) with strength less than that of mortar. Physical and mechanical properties of concrete with dense coarse aggregate are presented in Table 1 and the concretes with the porous coarse aggregate in Table 2. The decrease of entrained air content with the increase of coarse aggregate concentration ϕσt were determined both for concretes with dense and porous coarse aggregate. The entrained air has a significant effect on concrete strength—1% of entrained air decreases the strength of concrete about 5% [11]. The influence of the coarse aggregate concentration on the compressive strength of concrete with the constant air content is presented in Figs 3 and 4. With the increase of coarse aggregate concentration the concrete strength decreases when the entrained air content in concrete is constant. The main reasons of the concrete strength reduction are the stress concentration and structural defects near the coarse aggregate. Coarse aggregate affects the structure of mortar. Dense coarse aggregate has negligible water absorption and does not change water content in mortar of concrete, and capillary porosity of mortar remains constant when the concentration of dense coarse aggregate ϕ st increases (Fig 5). Porous coarse aggregate (expanded clay aggregate) has large water absorption (more than 16%), therefore water content in mortar of concrete is reduced and capillary porosity of mortar is significantly reduced when the concentration of porous coarse aggregate ϕ st increases (Fig 5). The entrained air content in mortar with both dense and porous coarse aggregate decreases inverse proportionally to coarse aggregate concentration ϕ st (Fig 6). The investigations have shown that suitable selection of properties and volumetric concentration of coarse aggregate can reduce stress concentration in concrete and increase the concrete strength.

NDE ultrasonic methods to characterise the porosity of mortar

Premature damage of mortar and concrete structures, due to environmental action, demands procedures to estimate durability of this type of components. Mortar or concrete composition (e.g. grain size, type and percentage of sand) may have some influence in the durability, but it is mainly related to porosity, which determines the interaction between aggressive agents and material. In this work, several IDE ultrasonic methods to estimate porosity of mortar are presented and evaluated. In these methods, porosity is related to (1) the material structural noise, (2) sound velocity and (3) ultrasonic attenuation. In all these methods, mortar is consider to be formed by only two phases: solid and pores.

石灰石微粉末を添加したモルタルの中性化速度に関する一考察

Carbonation of mortar was examined when limestone powder was substituted for cement, water and sand.In addition, the influence of factors such as total porosity, air content and unit cement content oncarbonation of mortar were considered. The total porosity of mortar defined in this paper as porosity which includes the influence of air content is an important consideration of carbonation. The amount of carbon dioxide which penetrates mortar is determined by its total porosity. The carbonation coefficient decreases linearly with a decrease in total porosity, due to the linear decrease of carbon dioxide penetrating the mortar. The penetration rate of carbon dioxide is controlled by the unit cement content. As a result, the carbonation coefficient is inversely proportional to the unit cement content of mortar.

The properties of Portland cement-limestone-silica fume mortars

This work has studied the influence of the combined action of silica fume and limestone on strength development, porosity, pore structure and morphological features in the system where 15 wt% of cement was substituted by finely ground limestone. Silica fume was added in amounts of 0, 2, 5, 8, 11 and 15 wt% on a cement basis, respectively. It has been established that limestone addition considerably increases the total porosity of mortars. However, if introduced together with silica fume up to 8 wt% of silica, porosity decreases. More than 8 wt% of silica increases the porosity again. The cement mortar containing 8 wt% of silica fume shows the highest compressive strength, the minimum value of the total porosity, and its pore size distribution curve shows a discontinuous pore structure. Limestone is taken up to the system and reacts with aluminate and ferrite phases from cement. Approximately 5 wt% is available for reaction after 120 days hydration of mortars containing no silica fume. The quantity of limestone incorporated is affected by the silica fume content. The replacement of Portland cement by 15 wt% of silica fume causes reduction both in the amount of cement and in the free CH content available for limestone chemical activity, and in this condition limestone acts only as a filler addition.

Relationship Between Pore Structure and Mechanical Properties of Ordinary Concrete Under Bending Fatigue

Progressive macro damage of concrete under fatigue loading is caused by the change of its internal micro-meso properties such as pore structure. In this study, porosity, pore size distribution, and specific surface area of ordinary concrete at different fatigue stages were investigated using mercury intrusion, helium flow, and nitrogen adsorption (BET) methods. These properties changed with increasing loading cycles and could be taken as micro-meso damage parameters to evaluate macro fatigue damage of concrete. Test results showed that both porosity in mortar (mainly macro pores) and interface between mortar and coarse aggregates (interfacial cracks) developed at a similar rate. The corresponding residual bending fatigue strength and dynamic bending Young’s modulus were also obtained and their relationships with these micro-meso properties were established. The “intrinsic bending strength” and “intrinsic bending Young’s modulus” were predicted from these relationships.

Influence of KOH solution on the hydration and carbonation of high alumina cement mortars

The influence of KOH presence on the evolution of hydration and carbonation of high alumina cement mortars at two different curing temperatures (4 and 40 °C) has been studied. It has been confirmed that hydration reactions at both temperatures are accelerated with KOH presence and it has a great influence on hydrated and carbonated species. The massive deposition of carbonation products leads, in all cases to a decrease in mortar porosity which leads to an increase of mechanical strengths.

On the correlation between porosity and strength in high-alumina cement mortars

The evolution in time of the strength and porosity of mortars made with the same type of high-alumina cement and two different types of aggregate, calcareous and siliceous, is studied, and the effects of aggregate composition on both parameters are analysed. It is found that between strength and porosity a linear correlation exists. The effects of pore diameter on such correlation is investigated and it is ascertained that the best correlation can be obtained for total cumulative porosity. The results show that this correlation can be useful for the determination of compressive strengthin situ.

Factors influencing electrode potential of steel in concrete

Abstract An investigation of the rusting of steel wire in concrete and mortar is reported. Steel corrosion was monitored using electrode potential measurements, and five experimental parameters were controlled: cement type, mortar porosity, mortar cover thickness, mortar cracking, and carbonation thickness. Measurements were made by connecting the reference electrode to three locations on each face of every reinforced mortar parallelepiped sample. The results showed that the mean value of the electrode potential for a sample is correlated with the degree of rusting of the steel, although the location of the measurement does have some effect on the recorded electrode potential. Cracking of the mortar has also been shown to influence the electrode potential.

On the role of free calcium oxide in expansive cements

Results of research, tending to elucidate the effect of free CaO content in portland cement clinker upon the expansion of specimens of expansive cements, prepared in semi-commercial scale by intergrinding of portland cement clinker, C 4A 3 S -phase containing special clinker and gypsum, by means of examination of liquid phase composition and porosity of mortars, have been presented. Special clinker was obtained by burning a mix of limestone, fly ash with high Al 2O 3 content and gypsum. Obtained results confirm the advantageous effect of free lime upon the hydration process and properties of expansive cements. The concentration of CaO in the liquid phase seems to influence rather the rate of ettringite formation than the size of its crystals.