Pore Size Distribution Of Mortars Research Articles

Effect of ion chelator on water sorption and transport behavior of unsaturated mortars with high volume fly ash and blast furnace slag

This paper investigated the effect of ion chelator on water dependency of water transport and fixation in mortars with high volume of fly ash (FA) and blast furnace slag (BFS). Ion chelator (CA) as a new type of crystalline admixture could improve self-healing performance of cementitious materials by crack-healing and pore filling. The porosity of mortar was measured by vacuum saturation and pore size distribution of mortar was tested by low-field nuclear magnetic resonance (LF NMR). The water sorption of mortar was evaluated by water vapor adsorption desorption balance. The water transport of mortar with and without crack was tested by capillary water absorption. Based on the experimental results, the water distribution of capillary water absorption in mortar was calculated. Results showed that the pore structure of mortar was improved evidently by CA, and the pores (>1μm) and the total porosity in mortar containing 50 %BFS were significantly reduced. CA had no obvious effect on the water vapor diffusion coefficient of mortar, but has a significant impact on the liquid water diffusion coefficient, especially in pure cement and containing 50 % BFS mortar. The total capillary water absorption and capillary absorption coefficient of mortars were reduced by CA, especially in pure cement and containing 50 % BFS mortar. The addition of CA decreased the water penetration in mortar, the reduction rates of water penetration depth in experimental groups (with CA) at 360 min were 12.4 % (100 %OPC), 6.0 % (30 %FA), 21.3 % (50 %BFS) and 10.8 % (16 %FA 24 %BFS) compared to control group (no CA). After curing for 42d, the normalized water absorption coefficients S” of cracked M100CA and M50BFS50CA were 55.1 % and 72.0 %, respectively. Ion chelator significantly improved internal pore structure and crack healing ability of the mortar containing 50 %BFS, and then delayed the water diffusion.

Effect of temperatures on self-healing capabilities of concrete with different shell composition microcapsules containing toluene-di-isocyanate

The ambient temperatures have significant effect on self-healing capabilities of concretes with microcapsules. Self-healing capabilities of mortars with different shell composition (paraffin, paraffin/PE wax and nano-SiO2/paraffin/PE wax) microcapsules containing toluene-di-isocyanate under the temperature of 10 °C, 30 °C, 50 °C and 60 °C were investigated in this paper. The compressive strength, chloride diffusion coefficient and pore size distribution of mortars containing microcapsules before and after self-healing were characterized by mechanical property test, rapid chloride migration test and nuclear magnetic resonance, respectively. The crack healing ratio of mortars during self-healing period were measured. The self-healing capabilities of mortars containing different microcapsules raised with the increase from 10 °C to 50 °C. Nevertheless, when the temperature reached 60 °C, the self-healing capability of the mortar containing paraffin microcapsules (AM1) decreased obviously, while the self-healing capabilities of the mortars containing paraffin/PE wax microcapsules (AM2) and nano-SiO2/paraffin/PE wax microcapsules (AM3) were almost unchanged. The self-healing capability of AM3 was superior to that of AM1 and AM2 at the same temperature. The compressive strength recovery rate, chloride diffusion coefficient recovery rate and harmful pores ratios of AM3 after pre-damaged at 50 °C for 7 d self-healing were 94.1%, 81.2% and 47.3%, respectively. When the ambient temperature reached 50 °C, the surface cracks of the mortar with three kinds of microcapsules could be completely self-healed in 5 h. However, when the temperature raised to 60 °C, the healing ratio of the crack in AM1 with a width of 0.4–0.5 mm decreased to 49.52% after 6 h self-healing. Meanwhile, the surface cracks of AM3 could be completely self-healed less than 3 h.

Effect of Graphene Oxide/Graphene Hybrid on Mechanical Properties of Cement Mortar and Mechanism Investigation

This paper evaluated the effect of graphene oxide/graphene (GO/GR) hybrid on mechanical properties of cement mortar. The underlying mechanism was also investigated. In the GO/GR hybrid, GO was expected to act as a dispersant for GR while GR was used as reinforcement in mortar due to its excellent mechanical properties. For the mortar specimen, flexural and compressive strength were measured at varied GO to GR ratios of 1:0, 3:1, 1:1, 1:3, and 0:1 by keeping the total amount of GO and GR constant. The underlying mechanism was investigated through the dispersibility of GR, heat releasing characteristics during hydration, and porosity of mortar. The results showed that GO/GR hybrid significantly enhanced the flexural and compressive strength of cement mortars. The flexural strength reached maximum at GO:GR = 1:1, where the enhancement level was up to 23.04% (28 days) when compared to mortar prepared with only GO, and up to 15.63% (7 days) when compared to mortar prepared with only GR. In terms of compressive strength, the enhancement level for GO:GR = 3:1 was up to 21.10% (3 days) when compared with that of mortar incorporating GO only. The enhancement in compressive strength with mortar at GO:GR = 1:1 was up to 14.69% (7-day) when compared with mortar incorporating GR only. In addition to dispersibility, the compressive strength was also influenced by other factors, such as the degree of hydration, porosity, and pore size distribution of mortar, which made the mortars perform best at different ages.

Pore size distribution of mortars produced with agroindustrial waste

Abstract Sugarcane bagasse ash sand (SBAS) is an agroindustrial waste from the sugarcane industry. The aim of this study is to analyse the differences between the pore size distribution of mortars produced by partially replacing natural sand with SBAS. The following techniques are used: X-ray computed tomography, mercury intrusion porosimetry, and petrographic analysis. The tomography results show that mortars produced with SBAS contain fewer pores in the ranges 60–80 μm and 100–300 μm than mortar without SBAS. In particular, SBAS reduces macropores larger than 0.1 μm. An SBAS content of 30% replacing fine sand contributes to a 44% reduction of pores larger than 0.1 μm. The results show that SBAS incorporation changes the pore size distribution without affecting the porosity of the mortars.

Study of the substitution of limestone filler with pozzolanic additives in mortars

In this work several specimens of mortars were prepared with the addition of 5% fly ash and 5% perlite and their mechanical properties and porosity were tested and compared to those of mortars with no additives (reference sample). Specifically, it was studied the influence that these additives have on the elastic modulus and porosity of the mortars. After conducting chemical, mineralogical and granulometric analysis of additives, a series of measurements were made in fresh and hardened mortars. In fresh mortars, measurements were conducted according to the EN1015-2/3/8 Standards concerning flow value, wet bulk density, air content, water demand and water retention. In hardened mortars, the measurements were made in the age of 28 days. The rate of carbonation and the formation of hydraulic phases were investigated using XRD, scanning electron microscopy (SEM) and thermal analysis (DTA–TGA). Porosity and pore size distribution of mortars were investigated by mercury intrusion porosimetry. Compressive and bending strength and adhesion were measured according to the EN1015-11/12 Standards. Finally, the Young’s elastic modulus was measured in cylindrical specimens sized 50/100 mm (diameter/height) according to ASTM C469-02 Standard. The results of the present study indicated a differentiation in the microstructure of the mortars that can be contributed to the use of different additives, such as fly ash and perlite. The three materials proved to be compatible in their mechanical behavior and appropriate for construction use. The modulus of elasticity value is related to the ratio of compressive to flexural strength and in particular, with the increase of the value of the ratio, the value of the Young’s modulus of elasticity increases. The development of the microstructure represents a major parameter to improve existing mortars and to formulate new mortars.

A discussion of the paper “Study on the pozzolanic properties of rice husk ash by hydrochloric acid pretreatment” by Q. Feng, H. Yamamichi, M. Shoya, S. Sugita

This brief commentary discusses a recent study (Feng et al, 2004) on the pozzolanic properties of rice husk ash by hydrochloric acid pretreatment. In the study, the heat evolution and the hydration heat of cement, the Ca(OH)2 content in the mortar and the pore size distribution of mortar were determined. The results showed that pozzolanic activity of rice husk ash (RHA) is not only stabilized but also enhanced by pretreatment. In this commentary, Demirbas notes that the very high surface area of RHA increases its pozzolanic activity to compete with those of much finer admixtures. Demirbas calls for additional attention on the chemical effects of pozzolanic materials on crystal formation during the hydration. Demirbas also refers readers to another study in which the pozzolanic properties of hydrochloric acid-treated RHA were systematically investigated (Yalcin and Sevinc, 2001).

Reply to the discussion by Ayhan Demirbas of the paper “Study on the pozzolanic properties of rice husk ash by hydrochloric acid pretreatment”

In this article, Feng et al reply to a brief commentary on their recent study (Feng et al, 2004) on the pozzolanic properties of rice husk ash by hydrochloric acid pretreatment. In the study, the heat evolution and the hydration heat of cement, the Ca(OH)2 content in the mortar and the pore size distribution of mortar were determined. The results showed that pozzolanic activity of rice husk ash (RHA) is not only stabilized but also enhanced by pretreatment. In the commentary, Demirbas noted that the very high surface area of RHA increases its pozzolanic activity to compete with those of much finer admixtures. Demirbas called for additional attention on the chemical effects of pozzolanic materials on crystal formation during the hydration. Demirbas also referred readers to another study in which the pozzolanic properties of hydrochloric acid-treated RHA were systematically investigated (Yalcin and Sevinc, 2001). In their reply, the study authors agree with the comment that the chemical effects of pozzolanic materials on crystal formation and development during hydration should be expanded. The authors also provide some additional details regarding the pore distribution of rice husk ashes. They conclude by stressing that many more studies of this agricultural waste material need to be carried out.

Study on the pozzolanic properties of rice husk ash by hydrochloric acid pretreatment

The pozzolanic properties of rice husk ash by hydrochloric acid pretreatment are reported in the paper. Three methods have been used to estimate the pozzolanic activity of rice husk ash. The heat evolution and the hydration heat of cement, the Ca(OH) 2 content in the mortar and the pore size distribution of mortar are determined. It is shown that compare with the rice husk ash heated untreated rice husk, the sensitivity of pozzolanic activity of the rice husk ash heated hydrochloric acid pretreatment rice husk to burning conditions is reduced. The pozzolanic activity of rice husk ash by pretreatment is not only stabilized but also enhanced obviously. The kinetics of reaction of rice husk ash with lime is consistent with diffusion control and can be represented by the Jander diffusion equation. A significant increase in the strength of the rice husk ash (pretreated) specimen is observed. The results of heat evolution indicate that the rice husk ash by pretreatment shows the behavior in the increase of hydration of cement. The cement mortar added with the rice husk ash by pretreatment has lower Ca(OH) 2 content after 7 days and the pore size distribution of the mortar with the rice husk ash with pretreatment shows a tendency to shift towards the smaller pore size.

Pore size distribution and compressive strength of waste clay brick mortar

This paper reports the results of an investigation of the pore size distribution of mortar that contains varying amounts of ground brick from different European brick types. Clay brick deriving from four European countries was ground to roughly cement fineness and used to partially replace cement in quantities of 0%, 10%, 20% and 30% in standard mortars. The pore volume, pore size distribution, threshold radius and strength of these mortars were tested for curing periods of up to one year. The presence of ground brick (GB) alters significantly the compressive strength of mortar and this is attributed to both the dilution effect and production of additional C–S–H gel from reaction of GB with CH. The additional C–S–H gel refines the pore size distribution of the mortar and this is reflected in compressive strength values obtained for these mixes. A critical relationship between threshold radius and compressive strength is also observed.

建設材料 コンクリート構造物の鉄筋腐食に関する複合要因の影響

Some kinds of reinforced concrete structures in the natural environmental condition suffered from damages due to combined causes, i.e. chloride corrosion, carbonation, alkali-aggregate reaction (AAR), and so on. In this study, it is tried to clarify the effects of these combined deteriorating causes on the steel bar corrosion and durability of concrete structures. The first objective of this study is to investigate the effects of water cement ratio, AAR and chloride content on carbonation in concrete. The second one is to make clear the microstructure of concrete affected by combined causes. The pore volume and pore size distribution of mortar were determined by a mercury penetration method. The test results are summerized as follows; (1) The carbonation rate in concrete is not affected by the chloride content. This phenomenon is proved from the results obtained by the pore distribution measurement. (2) The carbonation rate and microstructure of concrete are affected largely by water cement ratio. (3) The chloride corrsion of reinforcing steel is accelerated by the degree of carbonation.