Sulphate-resisting Portland Cement Research Articles

Performance of Portland limestone cements in mortar prisms immersed in sulfate solutions at 5 °C

The results of a test programme to investigate the sulfate resistance of mortars, immersed up to 12 months at 5 °C in magnesium sulfate and sodium sulfate solutions, is described. The mortars were prepared from four cements; a Portland cement, a sulfate-resisting Portland cement and two Portland limestone cements containing 15% by mass of an oolitic limestone and a carboniferous limestone. The mortar specimens were subject to BS 5328 Class 4A and 4B sulfate exposure conditions. These are the highest classes for concretes prepared using sulfate-resisting Portland cement (SRPC) before surface protection is required and are two and three classes higher than those recommended for concretes prepared using Portland cement (PC) and Portland limestone cement (PLC), respectively. Two free water-cement ratios were used, 0.5 and 0.75. Performance was monitored by visual assessment, expansion and changes in flexural and compressive strengths. At a free water-cement ratio of 0.75, the PC mortars and PLC mortars exhibited visually very severe attack with the former showing expansion and reductions in strength, and the latter mainly reductions in strength. At a free water-cement ratio of 0.50 both the PC mortars and PLC mortars showed slight/moderate to severe visual attack, the degree of deterioration appearing slightly greater in the PLC mortars, more especially those made with oolitic limestone. The PLC mortars also exhibited reductions in compressive failure load. The SRPC mortars exhibited little visual deterioration, no expansion, a small increase in flexural strength and no significant reductions in compressive strength. At a free water-cement ratio of 0.75 substantial amounts of thaumasite, together with ettringite was present in the surface layers of the deteriorated PLC mortars whilst ettringite was present in the surface layers of the deteriorated PC mortars. It is concluded that mortars made with a PC with a C 3A content of about 10% by mass were broadly similar in their vulnerability to sulfate attack at 5 °C as PLC mortars containing 15% limestone by mass, although the mode of attack was different.

Corrosion of reinforcement steel embedded in high water-cement ratio concrete contaminated with chloride

The aim of this investigation was to examine the role of internal chloride on the corrosion behaviour of steel in ordinary Portland cement (OPC), and sulphate resistant Portland cement (SRPC) mortar mixes of higher water-cement (w/c) ratios. For this purpose, the steel electrodes embedded in mortar specimens were subjected to short-term electrochemical monitoring. On completion of electrochemical monitoring, pore solution was extracted from the specimens for analysis. For the purpose of comparison, pore solution was also extracted from separate OPC and SRPC cylindrical mortar specimens hydrated in an environment isolated from the atmosphere. Results from microanalysis using scanning electron microscope (SEM) are also reported. The results demonstrated that mortars prepared with a cement of high tricalcium aluminate (C 3A) content, even when the w/c ratio of the mix was maintained at 0.70, still passivated the steel embedded in it even in the presence of chloride as high as 1% by weight of cement. Under a similar condition, the steel embedded in mortar prepared with a cement of low C 3A content was unable to passivate the steel electrode. The special protection mechanism by the lime-rich layer as proposed by Page for low w/c ratio concretes is also valid for the steel embedded in high w/c ratio mortar. The type of exposure condition (e.g. exposure to atmosphere) during the hydration period strongly influences the hydroxide ion concentration in the pore solution, while this has no effect on the freechloride concentration in the pore solution. This study reconfirms the significance of the C 3A phase of cement in respect to chloride-binding processes.

Attack of Concrete Floors in Pig Houses by Feed Acids: Influence of Fly Ash Addition and Cement-bound Surface Layers

Abstract Concrete floors in pig houses are subject to attack by lactic and acetic acid, formed in spilled and soured meal–water mixtures. Accelerated degradation tests, comprising cyclical exposure to acidic liquids and detachment of the unstable concrete by brushing, were used to simulate the attack of concrete floors and of cement-bound surface layers. It is estimated that the effect of one attack cycle on the reference concrete is more or less equivalent to the floor degradation observed in houses for fattening pigs at the most vulnerable place in front of a wetfeeder after one to two years. It was found that the addition of about 10% low-calcium coal fly ash by weight of cement to a high-quality concrete made with ordinary portland cement (OPC), reduced the degradation significantly. The addition of fly ash to concrete made with sulphate-resisting portland cement (0%C 3 A) mostly resulted in less deterioration than addition to concrete made with ordinary portland cement during the first stage of the attack. However, the differences were seldom significant after two attack cycles. Under very highly aggressive exposure, a surface layer (mortar) consisting of the product S (based on ground tuff) and blast-furnace slag cement showed the best resistance.

Geotechnical properties of fresh cement grout—pressure filtration and consolidation tests

This technical note examines the effects of removing water from a fresh cement suspension by pressure filtration, which turns the slurry into a material having significant effective stresses; it also clarifies some aspects of the consolidation behaviour of this filtered material. The test series covered: (1) a sulphate-resisting Portland cement (SRC); (2) an ordinary Portland cement (OPC); and (3) a super-fine Portland cement (MFC). They were all normal cements, obtained in 25kg batches. The experiments were like one-dimensional consolidometer tests with top drainage only, but used a slurry as starting material. The usual assumptions for one-dimensional consolidation analysis were made, and the filter cake was also treated as a stiff uniform layer. In the experimental procedure, the grout was mixed for a time in a high-shear disperser, then transferred to a consolidometer tube lubricated with mould release oil, with one layer of tissue and two layers of filter paper placed carefully on top of the grout. A displacement transducer measured the piston movement. Charts and tables are presented for the results of the filtration and consolidation tests. The analysis and data are required for quantitative assessment of construction effects, due to cement grouting or concrete placement in the ground.

Interaction of Eu(III) and Th(IV) With Sulfate-Resisting Portland Cement

ABSTRACTThe uptake of Eu(III) and Th(IV) by a sulphate-resisting Portland cement has been investigated in batch type sorption experiments using 152 Eu and 234Th as tracers. Prior to performing sorption studies, the experimental methodology was assessed. The kinetics of Eu(III) and Th(IV) interactions with cement were measured for times up to about 130 days. The effect of isosaccharinic acid added to artificial cement pore water on Eu(III) and Th(IV) uptake was examined to elucidate the effect of cellulose degradation products.

Microstructural and microanalytical studies of sulfate attack. V. Comparison of different slag blends

Pastes of several slag blends that had been stored in 0.25 mol I −1 solutions of sodium or magnesium sulfate were studied by scanning electron microscopy using backscattered electron (BSE) imaging and X-ray microanalysis of polished sections. In general, attack resulted in decalcification of C-S-H and the formation of ettringite. With Na 2So 4, little or no gypsum was formed, but with MgSO 4, brucite, poorly crystalline serpentine (M 3S 2H 2) and gypsum were also formed. Visual examinations and BSE images indicated that the relative susceptibility of the blends to attack by Na 2SO 4 increases with the content of Al 2O 3 available for the formation of ettringite; this includes that present in AFm phases but not that present in C-S-H or hydrotalcite. The rank order of susceptibility to attack by MgSO 4 was broadly similar to that by Na 2SO 4, but the slag blends performed more poorly relative to plain Portland cement or sulfate-resisting Portland cement. Resistance to attack by Na 2SO 4, is favoured by the use of high proportions of slag, slags low in Al 2O 3, or sulfate resisting Portland cements and by supplementing the gypsum in the Portland cement component by additional calcium sulfate.

A discussion of the paper “microstructural and microanalytical studies of sulfate attack. II. Sulfate-resisting portland cement: Ferrite composition and hydration chemistry” by R.S. Goliop and H.F.W. Taylor

A discussion of the paper “microstructural and microanalytical studies of sulfate attack. II. Sulfate-resisting portland cement: Ferrite composition and hydration chemistry” by R.S. Goliop and H.F.W. Taylor

A reply to a discussion by J.S. Lota, (the late) P.L. Patt and J. Bensted of the paper “microstructural and microanalytical studies of sulfate attack. II. Sulfate-resisting portland cement: Ferrite composition and hydration chemistry”

A reply to a discussion by J.S. Lota, (the late) P.L. Patt and J. Bensted of the paper “microstructural and microanalytical studies of sulfate attack. II. Sulfate-resisting portland cement: Ferrite composition and hydration chemistry”

Microstructural and microanalytical studies of sulfate attack III. Sulfate-resisting portland cement: Reactions with sodium and magnesium sulfate solutions

Cubes of a sulfate-resisting Portland cement (SRPC) paste that had been stored for 6 months in solutions of Na 2SO 4 or MgSO 4 were examined by scanning electron microscopy using backscattered electron imaging and X-ray microanalysis. The changes observed were broadly similar to those which we have found with a normal Portland cement (PC), but cracking and loss of material were less marked, less ettringite was formed, and decalcification of the CSH was much reduced. As with the PC, gypsum was formed, both in veins and mixed with the CSH. The differences are attributed to the low content of Al 2O 3 in the hydration products of the SRPC, and to the fact that some of the Al 2O 3 is already present as ettringite. The decreased formation of ettringite and decreased decalcification of the CSH in the SRPC together explain the superior resistance to sulfate attack.

Deterioration of reinforced concrete in the marine industrial environment of the Arabian Gulf—A case study

This paper describes the deterioration of reinforced concrete structures at a liquefied gas/sulfur plant that occurred shortly after completion of the construction. Investigations have shown that the principal cause of the deterioration was corrosion of reinforcing steel due to the presence of chlorides, with marine salts being the main source. The primary contributing factor was the increased level of industrial pollutants which, in combination with marine salts, rendered the plant environment highly aggressive to the reinforcement. Other contributing factors included the use of sulfate resisting Portland cement, the presence of hairline cracks in the concrete, the elevated water/cement ratio, and insufficient concrete cover. The problem of corrosion was also aggravated by simultaneous action of multiple environmental factors, such as the high salinity of Gulf water with a consequent high rate fallout of marine salts, high relative humidities and air temperature over much of the year unfavourable wind speed and direction, intense solar radiation, and corrosive ground conditions. Considering all the data available, it appears that the corrosion process in reinforcing steel at the liquefied gas/sulfur plant is a result of complex synergistic effects of chlorides and acid solutions enhanced by the unfavourable environmental conditions prevailing in the region.

Pore size distribution of OPC & SRPC mortars in presence of chlorides

The pore structure of chloride-free ordinary portland cement(OPC) and sulphate resistant Portland cement(SRPC) mortars are compared with the corresponding mortars with NaCl and CaCl 2 added during mixing. In both OPC and SRPC mortars the addition of chlorides reduced the total accessible pore volumes compared to the corresponding chloride-free mortars. Also, in the presence of chlorides, the number of coarse pores were increased. These changes in the pore structure are believed to be due to dense calcium silicate hydrate(C-S-H) gel morphology formed in the presence of chlorides. The SRPC showed greater changes in pore structures than the OPC with equivalent amounts of chlorides added. This may be due to the lower chloride binding capacity of the SRPC and hence the higher availability of free chlorides to modify the gel morphology.

The binding of chloride ions by sulphate resistant portland cement

The relative tendency of different portland cements to remove chloride ions from the mix water by forming chloro-complexes is an important factor in the study of the corrosion of the embedded steel. The tri-calcium aluminate (C 3A) phase of the ordinary portland cement (OPC) plays a dominant role in binding the chloride ions, but little quantitative information is available in the literature concerning the relative influence of the tetra-calcium aluminoferrite (C 4AF) phase of the cement. The present investigation is an attempt to elucidate the role of C 4AF in the sulphate resistant portland cement with respect to chloride binding. It is concluded that the chlorides in SRPC are bound in the form of the chloro-complex C 3F.CaCl 2.10H 2O which is derived from the C 4AF phase of the cement.

Microstructural and microanalytical studies of sulfate attack. II. Sulfate-resisting Portland cement: Ferrite composition and hydration chemistry

A sulfate-resisting Portland cement and pastes made from it were studied by X-ray microanalysis of polished sections in the scanning electron microscope, X-ray diffraction and thermal analysis. The ferrite phase had the approximate composition Ca 2Al 0.8Mg 0.2Si 0.2O 5 with minor substitutions of Fe by Ti and Mn. The hydration products other than CSH and calcium hydroxide were small in amount and, for the most part, closely mixed with each other and with CSH. Ettringite was formed initially; some persisted for at least one year. Only a little monosulfate was formed. Mg appeared mainly to enter a hydrotalcite-type phase, and Fe a poorly crystalline hydrogarnet. Calculated X-ray powder diffraction patterns for the ferrite and hydrogarnet are given. Factors contributing to the superior resistance to sulfate attack include the low content of Al 2O 3 in the hydration products and the fact that much of this Al 2O 3 is present for a long time as ettringite. As a result, the potential for forming ettringite through reaction with sulfate from an external source is considerably less at all ages than is the case with an Ordinary Portland Cement.

The influence of binder type on sulfate resistance

Four sulfate resisting binder types have been examined by immersing mortar specimens (40∗40∗160 mm, sand/binder ratio = 3.0), in magnesium sulfate solutions. Strength, mass and length changes have been recorded over a period of 2 years. Differences in performance between SRPC and mixer combinations PC/blastfurnace slag, PC/fly ash and PC/silica fume binders have been vonfirmed, and the general conclusion of the study is that the sulfate resisting Portland cements behaved significantly better than these other binders under the conditions of exposure adopted.

Leaching of simulated heavy metal waste stabilized/solidified in different cement matrices

Leaching experiments have been carried out on samples of ordinary portland cement (OPC), sulphate-resistant portland cement (SRPC) with fly ash (FA) added and an alumina cement (AC), with each receiving various concentrations (0.1–1.0 M of chromium (Cr 6+), vanadium (V 5+) and cadmium (Cd 2+. The samples were prepared and evaluated with a statistical experimental matrix corresponding to a Box-Behnken fractional factorial design. Leaching was done in PTFE vessels using the standard TCLP (toxicity characteristic leaching procedure of the U.S. Environmental protection Agency). Analyses of the leachates were carried out for elements Cr, Cd, V, Si, Al, Ca and Fe by inductively coupled plasma spectroscopy. Selected solid samples were investigated before and after leaching by scanning electron microscopy, in conjunction with energy dispersive X-ray spectrometry, and by scanning transmission electron microscopy on thinned specimens. The normalized mass losses of chromium varied between 3.3 10 3-tand 3.5 10 1-t kg/m 2. Calculated maximum release was found for a hypothetical cement with approximately 20% alumina, while minimum release was found for AC with 36.7% alumina. The normalized mass losses of vanadium varied between 110 −3 and 810 −2 kg/m 2. Calculated maximum release was found for a hypothetical cement with approximately 25% alumina and minimum release was found for OPC. All samples of the cadmium series except three showed solution concentrations below the detection limit (0.1 ppm), suggesting very effective retention of this element by all three cement matrices investigated.

Sorption and diffusion studies in cementitious grouts

Laboratory experiments were conducted to evaluate the contaminant transport properties of cement-based sealing materials for use in vault sealing and fracture grouting within an underground repository for nuclear fuel waste. Diffusion coefficients were measured for tritiated water and 36Cl under simulated saline groundwater conditions for six mixtures of Sulphate Resistant Portland Cement and Silica Fume at two water to cement ratios. Tortuosity factors were calculated from the results of the diffusion tests and retardation factors for 137Cs and 85Sr were estimated from measured distribution coefficient, bulk density, and porosity values. The results of the diffusion experiments show both tritiated water and 36Cl to behave as reactive tracers in cement-based materials. The water to cement ratio was shown to have a significant effect on the retardation capabilities of the grout mixes with reatardation factors increasing as the water to solid ratio was reduced from 0.35 to 0.25. The results also showed the addition of silica fume to have impact on the potential migration rates of both 137Cs and 85Sr, however, under saline conditions, a similar reduction in the effective diffusion coefficients could be achieved through a decrease in the water to cement ratios.

A conduction calorimetric study of gasifier slag-portland cement blends

Gasifier slag (GS) is intermediate in chemical composition between granulated blast furnace slag (BFS) and pulverised fuel ash (PFA). A conduction calorimetric study has been made of three GS, blended with an ordinary Portland cement (OPC) and a sulphate-resisting Portland cement (SRPC). These results are compared with those of a BFS and a PFA blended with the same cements. The results for all three GS are very similar to those for BFS, with slight retardation of peak 2, and the presence of peak S. PFA shows significant retardation of peak 2, and the absence of peak S.

Sulphate attack on concrete

The types of disruption observed during sulphate attack on mortars or concretes, and the chemical processes involved, are summarized. Concrete mix design and binder type have an important influence on concrete performance in sulphate environments. The present UK Codes of Practice (based on BRE Digest 250) reflect the technical information available for various binders currently used in the UK. Sulphate-resisting Portland cement is a purpose-made cement designed to resist sulphates. The chemical factors giving rise to its sulphate resistance are well understood, and its performance has been uniformly good in experimental trials throughout the world. This cement is the standard by which other binders are judged, and should continue to be the preferred binder for concretes expected to withstand sulphate concentrations in ground waters greater than 3000 mg SO4− −/l. Although partial replacement of ordinary Portland cement (OPC) by various latent hydraulic binders can lead to improved sulphate resistance, the mechanism by which these latent hydraulic binders act is not established. There is well-documented evidence of considerable variability of performance for OPC/pulverized fuel ash and OPC/ground granulated blastfurnace slag combinations, and the ability of composite cements to provide a guaranteed performance is suspect. A more rigorous approach towards the selection of composite binder components in the appropriate standards is required before their use can be recommended in ground waters where sulphate levels exceed 3000 mg SO4− −/l.

Effect of chloride in mix ingredients on sulphate resistance of concrete

The sulphate resistance of concretes containing various levels of chloride introduced in the mixing water was assessed by immersion in sodium sulphate and magnesium sulphate solutions. Mortar and concrete cubes were made using ordinary Portland cement (OPC) and sulphate-resisting Portland cement (SRPC) with chloride contents of 0–4·5%; the chloride was introduced in a salt of either sodium or calcium. Deterioration was monitored by comparing the strength of cubes in sulphate solutions with that of similar cubes stored in water over a period of 7 years for concrete and of 1 year for mortar. The 100 mm concrete cubes (which were also assessed visually at 3 and 7 years) were made with two levels of cement content (225 and 335 kg/m3). A 1:3 cement/sand mix was used for the 12·5 mm mortar cubes. The results over 1 year for the mortar cubes showed that chloride had either a negligible or a generally beneficial effect on the resistance to sulphate attack for both OPC and SRPC. A similar overall trend was observed for the concrete cubes after 7 years, with the apparent exception of some concretes containing calcium chloride and immersed in strong sulphate solutions, for which sulphate resistance was considerably reduced.

The chemistry of Portland cement-gasifier slag interactions

Gassifier slag (GS) is a potential new cement replacement material which is intermediate in composition between granulated blastfurnace slag (GBFS) and pulverized fuel ash (P FA). Three GSs have been blended with an ordinary Portland cement (OPC) and a sulphate-resisting Portland cement (SRPC) , and comparisons made with a G BFS and a P FA blended with the two cements. Several techniques have been used to investigate the slag-cement interactions in both the early and later stages of hydration. The results indicate that, like GBFS, GS cements show latent hydraulic activity, particularly in the early stages of hydration, while, as with PFA, pozzolanic activity dominates in the later stages.