The porosity and pore size distribution of cured OPC-metakaolin paste has been investigated. Past... more The porosity and pore size distribution of cured OPC-metakaolin paste has been investigated. Pastes containing 0,5,10 and 15% metakaolin were prepared at a constant water/binder (wb) ratio of 0.55. Specimens were moist cured for periods from 3 to 365 days. The intruded pore volume and the pore structure were determined by mercury intrusion porosimetry. The proportion of large pores (radius > 0.02) in the paste decreases with both increase in metakaolin content and increase in curing time. Although the total intruded pore volume generally decreases with increase in curing time it is found to increase with increase in metakaolin content. Also an increase in pore volume is observed between the curing times of 14 and 28 days for pastes containing metakaolin. This latter observation is explained in terms of two possible mechanisms.
Cement mortars and pastes containing 0, 5, 10 and 15% replacement of cement with metakaolin and w... more Cement mortars and pastes containing 0, 5, 10 and 15% replacement of cement with metakaolin and with a water/binder (w/b) ratio of 0.55 have been moist cured for periods from 3 to 365 days. The Portlandite content at different ages has been determined by thermogravimetric ...
The porosity and pore size distribution of cured OPC-metakaolin paste has been investigated. Past... more The porosity and pore size distribution of cured OPC-metakaolin paste has been investigated. Pastes containing 0,5,10 and 15% metakaolin were prepared at a constant water/binder (wb) ratio of 0.55. Specimens were moist cured for periods from 3 to 365 days. The intruded pore volume and the pore structure were determined by mercury intrusion porosimetry. The proportion of large pores (radius > 0.02) in the paste decreases with both increase in metakaolin content and increase in curing time. Although the total intruded pore volume generally decreases with increase in curing time it is found to increase with increase in metakaolin content. Also an increase in pore volume is observed between the curing times of 14 and 28 days for pastes containing metakaolin. This latter observation is explained in terms of two possible mechanisms.
The sulphate resistance of mortar containing ground calcined brick clay (GCBC) calcined at differ... more The sulphate resistance of mortar containing ground calcined brick clay (GCBC) calcined at different tempertaures (600-l 1OOT) and ground sand (GS) as cement replacement materials is investigated. Also the porosity, pore size distribution and strength of a selection of these mortars are determined. Mortars containing GCBC calcined at a temperature higher than 900°C show superior sulphate resistance to those containing GCBC calcined at temperatures below 900°C. Although the intruded pore volume is higher at early ages of curing, the inclusion of GCBC in the mortars leads to refmement of pore structure and its contribution to strength is significant after a curing period of 90 days. The influence of the incorporation of GCBC (calcined at different temperatures) on the sulphate resistance of mortar, is discussed in terms of fundemental mechanisms. 0 1997
The partial substitution of cement (both high C 3 A and intermediate C 3 A) with metakaolin (MK) ... more The partial substitution of cement (both high C 3 A and intermediate C 3 A) with metakaolin (MK) is investigated in terms of resistance of MK mortar to sodium sulphate (Na 2 SO 4 ) solution. Results on strength, porosity, pore size distribution, and calcium hydroxide (CH) contents are also reported. The sulphate expansion results demonstrate that the sulphate resistance is increased as the replacement level of cement with MK increases, up to at least 25% replacement. Refinement in pore structure and reduction in CH content increase with increase in MK content (for moist-cured mortar), and these two factors are considered to be the principal factors affecting improvement in sulphate resistance. Also, although after prolonged periods of exposure to Na 2 SO 4 solution, there is (relative to water-cured specimens) significant strength loss of PC mortars and mortars with low levels of MK (5 and 10%); for mortars with high levels of MK (15, 20 and 25%), there is consistent strength gain.
Sidney Diamond, in his paper on the limitations of mercury porosimetry in determining pore size d... more Sidney Diamond, in his paper on the limitations of mercury porosimetry in determining pore size distributions in cement-based materials [1], very effectively articulated what most people using the technique for this purpose already knew or at least suspected. This in no way detracts from the very eloquent way in which the author presented, in a convincing manner, the available evidence to demonstrate that the pore size distributions, obtained from mercury porosimetry of cement-based systems, considerably overestimate the volume of fine capillary pores and underestimate the volume of coarse capillary pores. That is, the cumulative pore volume versus pore diameter curves are much steeper than they ought to be and are shifted by one or two orders of magnitude to finer pore sizes.
Temperature-time profiles of mortar cubes have been determined using a semi-adiabatic curing meth... more Temperature-time profiles of mortar cubes have been determined using a semi-adiabatic curing method for curing times of 160 h. The binders employed were metakaolin-portland cement (MK-PC), fly ash-portland cement (PFA-PC) and MK-PFA-PC blends, with a maximum PC replacement level of 40% and MK levels of up to 15%. Relative to PC mortar (and as previously reported by other workers), MK-PC mortars show an enhanced temperature-rise whereas in PFA-PC mortars the temperature-rise is depressed. In ternary mortars MK and PFA have a compensatory effect. Both MK and PFA delay the time taken to reach the peak temperature with MK producing the greatest delay. Partial substitution of MK for PC has only a minor influence on the total heat evolved by the mortar whereas partial substitution of PC with PFA produces a marked fall in the heat evolved. The temperature-rise of MK-PC mortars with respect to PC-mortar shows two distinct peaks which are attributed to a two-stage hydration effect. Ó
The thaumasite form of sulfate attack (TSA), is a deleterious physico-chemical attack of the calc... more The thaumasite form of sulfate attack (TSA), is a deleterious physico-chemical attack of the calcium silicate hydrate (C-S-H), binding phase of concrete. Water:binder ratios (w:b), are known to control ingress of potentially deleterious ions by pore structure refinement at low (0.40) values. Equally, a physical-chemical barrier exists at about w:b ratio of 0.45 regardless of the binder type. The inclusion of ultra-fine pozzalans (e.g. metakaolin) in the binder has been shown to impart such properties through densification of the matrix and removal of calcium hydroxide.
Existing data on the relationships between temperature, pozzolanic activity and cement hydration ... more Existing data on the relationships between temperature, pozzolanic activity and cement hydration are reviewed with particular emphasis on condensed silica fume (CSF)-ordinary Portland cement blends. CSF concrete with a range of fume contents has been cured at ...
The porosity and pore size distribution of cured OPC-metakaolin paste has been investigated. Past... more The porosity and pore size distribution of cured OPC-metakaolin paste has been investigated. Pastes containing 0,5,10 and 15% metakaolin were prepared at a constant water/binder (wb) ratio of 0.55. Specimens were moist cured for periods from 3 to 365 days. The intruded pore volume and the pore structure were determined by mercury intrusion porosimetry. The proportion of large pores (radius > 0.02) in the paste decreases with both increase in metakaolin content and increase in curing time. Although the total intruded pore volume generally decreases with increase in curing time it is found to increase with increase in metakaolin content. Also an increase in pore volume is observed between the curing times of 14 and 28 days for pastes containing metakaolin. This latter observation is explained in terms of two possible mechanisms.
Cement mortars and pastes containing 0, 5, 10 and 15% replacement of cement with metakaolin and w... more Cement mortars and pastes containing 0, 5, 10 and 15% replacement of cement with metakaolin and with a water/binder (w/b) ratio of 0.55 have been moist cured for periods from 3 to 365 days. The Portlandite content at different ages has been determined by thermogravimetric ...
The porosity and pore size distribution of cured OPC-metakaolin paste has been investigated. Past... more The porosity and pore size distribution of cured OPC-metakaolin paste has been investigated. Pastes containing 0,5,10 and 15% metakaolin were prepared at a constant water/binder (wb) ratio of 0.55. Specimens were moist cured for periods from 3 to 365 days. The intruded pore volume and the pore structure were determined by mercury intrusion porosimetry. The proportion of large pores (radius > 0.02) in the paste decreases with both increase in metakaolin content and increase in curing time. Although the total intruded pore volume generally decreases with increase in curing time it is found to increase with increase in metakaolin content. Also an increase in pore volume is observed between the curing times of 14 and 28 days for pastes containing metakaolin. This latter observation is explained in terms of two possible mechanisms.
The sulphate resistance of mortar containing ground calcined brick clay (GCBC) calcined at differ... more The sulphate resistance of mortar containing ground calcined brick clay (GCBC) calcined at different tempertaures (600-l 1OOT) and ground sand (GS) as cement replacement materials is investigated. Also the porosity, pore size distribution and strength of a selection of these mortars are determined. Mortars containing GCBC calcined at a temperature higher than 900°C show superior sulphate resistance to those containing GCBC calcined at temperatures below 900°C. Although the intruded pore volume is higher at early ages of curing, the inclusion of GCBC in the mortars leads to refmement of pore structure and its contribution to strength is significant after a curing period of 90 days. The influence of the incorporation of GCBC (calcined at different temperatures) on the sulphate resistance of mortar, is discussed in terms of fundemental mechanisms. 0 1997
The partial substitution of cement (both high C 3 A and intermediate C 3 A) with metakaolin (MK) ... more The partial substitution of cement (both high C 3 A and intermediate C 3 A) with metakaolin (MK) is investigated in terms of resistance of MK mortar to sodium sulphate (Na 2 SO 4 ) solution. Results on strength, porosity, pore size distribution, and calcium hydroxide (CH) contents are also reported. The sulphate expansion results demonstrate that the sulphate resistance is increased as the replacement level of cement with MK increases, up to at least 25% replacement. Refinement in pore structure and reduction in CH content increase with increase in MK content (for moist-cured mortar), and these two factors are considered to be the principal factors affecting improvement in sulphate resistance. Also, although after prolonged periods of exposure to Na 2 SO 4 solution, there is (relative to water-cured specimens) significant strength loss of PC mortars and mortars with low levels of MK (5 and 10%); for mortars with high levels of MK (15, 20 and 25%), there is consistent strength gain.
Sidney Diamond, in his paper on the limitations of mercury porosimetry in determining pore size d... more Sidney Diamond, in his paper on the limitations of mercury porosimetry in determining pore size distributions in cement-based materials [1], very effectively articulated what most people using the technique for this purpose already knew or at least suspected. This in no way detracts from the very eloquent way in which the author presented, in a convincing manner, the available evidence to demonstrate that the pore size distributions, obtained from mercury porosimetry of cement-based systems, considerably overestimate the volume of fine capillary pores and underestimate the volume of coarse capillary pores. That is, the cumulative pore volume versus pore diameter curves are much steeper than they ought to be and are shifted by one or two orders of magnitude to finer pore sizes.
Temperature-time profiles of mortar cubes have been determined using a semi-adiabatic curing meth... more Temperature-time profiles of mortar cubes have been determined using a semi-adiabatic curing method for curing times of 160 h. The binders employed were metakaolin-portland cement (MK-PC), fly ash-portland cement (PFA-PC) and MK-PFA-PC blends, with a maximum PC replacement level of 40% and MK levels of up to 15%. Relative to PC mortar (and as previously reported by other workers), MK-PC mortars show an enhanced temperature-rise whereas in PFA-PC mortars the temperature-rise is depressed. In ternary mortars MK and PFA have a compensatory effect. Both MK and PFA delay the time taken to reach the peak temperature with MK producing the greatest delay. Partial substitution of MK for PC has only a minor influence on the total heat evolved by the mortar whereas partial substitution of PC with PFA produces a marked fall in the heat evolved. The temperature-rise of MK-PC mortars with respect to PC-mortar shows two distinct peaks which are attributed to a two-stage hydration effect. Ó
The thaumasite form of sulfate attack (TSA), is a deleterious physico-chemical attack of the calc... more The thaumasite form of sulfate attack (TSA), is a deleterious physico-chemical attack of the calcium silicate hydrate (C-S-H), binding phase of concrete. Water:binder ratios (w:b), are known to control ingress of potentially deleterious ions by pore structure refinement at low (0.40) values. Equally, a physical-chemical barrier exists at about w:b ratio of 0.45 regardless of the binder type. The inclusion of ultra-fine pozzalans (e.g. metakaolin) in the binder has been shown to impart such properties through densification of the matrix and removal of calcium hydroxide.
Existing data on the relationships between temperature, pozzolanic activity and cement hydration ... more Existing data on the relationships between temperature, pozzolanic activity and cement hydration are reviewed with particular emphasis on condensed silica fume (CSF)-ordinary Portland cement blends. CSF concrete with a range of fume contents has been cured at ...
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