a rapid hardening cement based on high alumina cement

BRECEM: a rapid hardening cement based on high alumina cement

Proc. Instn Clv. Engrs Structs & Bldgs, 1994,104. Feb., 93-100

G. J. Osborne, LRSC

m The Building Resea rch Establishment (BRE) has developed a blended cement based on high a l u m i n a cement (HAC) wi th ground granulated blastfurnace slag. This cement has been given the t r a d e m a r k ‘ BRECEM ’ and the p roper t ies o f concrete m a d e f r o m the n e w cement are being studied at BRE in col labora t ion wi th the industry. In this Paper, the chemica l and thermal stabil i ty of BRECEM and HAC mortars a n d concretes is compared as a necessary prel iminary to de te rmin ing engineering propert ies in due course. Con- crete durabi l i ty s tud ies are at a n e a r l y stage a n d , as such, t h e uses f o r this c e m e n t are sti l l under development.

hydra t ion reactions in HAC. A chemical compound, gehlenite hydra te ( s t ra t l ing- ite), not seen in plain HAC in significant amounts , fo rms readi ly and becomes the major hydra t e cons t i t uen t in d u e course,

phase assemblage. Studies to determine a n d is thought to provide a more stable

the chemical and physical properties of BRECEM in mortars and concrete o v e r a

t i ons have been set u p at BRE. BRECEM range of temperatures and storage condi-

mortars show exce l len t su lpha te resistance. HAC and BRECEM concrete durabi l i ty specimens have performed very wel l following storage fo r a y e a r in aggressive sulphate , marine and sof t water environments . Longer term tests wil l be carr ied out at two, five and 10 years.

greater to l e rance to high w a t e r to cement ratio mix designs in forming s t ab le assemblages wi th reduced temperature rises and enhanced durabi l i ty , and there are cost savings compared with HAC concretes. A n u m b e r o f potential, practical applications h a v e been advocated.

Introduction Calcium aluminate or high alumina cement (HAC) is not used in structural applications in

from such cement shows reduction in strength the UK at the present time, as concrete made

with time under hot and humid conditions. This reduction in strength is associated with a set of chemical reactions, often referred to as ‘conversion’, that produce an increase in the porosity of concrete. Much has been written detailing the characteristics and performance of

The add i t ion o f s l ag a l t e r s t he course of

BRECEM concretes have shown a

HAC concretes (HACC), before and after the occurrence in the early 1970s of a relatively small number of roof collapses in the UK. The historical background to these failures and the decision to delete reference to HACC from the old Code ofpractice for the use ofstructural concrete (CP 110), now covered by British Stan- dards BS 8110, is dealt with in the paper by Currie and Crammond.‘ Their paper also gives current guidance and advice for the assessment of existing HACC construction in the light of research findings since 1975.

reduction in strength, which is characterstic of 2. Majumdar et al.’ showed that the inherent

HAC under normal service conditions,’ and is enhanced in hot and wet conditions, could be counteracted by adding to the cement a suffi- cient quantity of ground granulated blastfurnace slag. This new rapid hardening cement has been given the trademark ‘BRECEM’, and the properties of mortars and concretes made from it are being studied at the Building Research Establishment (BRE) in collaboration with the industry. The industrial partners are Lafarge Special Cements and the Cementitious Slag Manufacturers Assocation (CSMA).

3. The early studies have been devoted to

mortars and concretes, before specific applica- the assessment of the durability of BRECEM

engineering properties such as tensile and flex- tions are developed, which would then require

ural strength, shrinkage and creep to be determined within the longer term.

Development of BRECEM and how it differs from HAC

4. Before the collapse of a roof in Stepney, London, in 1974,’when HAC was written out of the British Standard Code for structural concrete (AMD 1553 in CP 110: 1972). HAC or Ciment Fondu had been used in many struC- tural applications where concrete needed rapid strength development and/or good chemical resistance. One of the principal causes of failure of HACC units is the reduction in its compressive strength with time, a condition which is accelerated in certain environments where hot and humid conditions prevail. Majumdar et d.’ showed that the effects of ‘conversion’ in HACC could be sufficiently counteracted, if not eliminated, by mixing a large proportion (typically 40-60%) of ground granulated blastfurnace slag (GGBS) with the cement to make BRECEM. They observed that in wet environments, the hydration of calcium

Building Croup Paper 10354

0 Crown copyright 1993

Establishment -Building Research

Written discussion closes 18 April I994

C.J. Osborne. Head of Concrete Durability Section, Building Research Establishment. Carston

OSBORNE

aluminates in HAC produced the mineral stratlingite, C,ASH, or 2Ca0 A1,0, SiO, 8H,O,* in the presence of GGBS, and that at temperatures higher than the ambient this phase became a major constituent of the hydrated cement in a matter of months. The formation of stratlingite, also known as gehlenite hydrate, plays a vital role in stabilizing and enhancing the long-term properties of BRECEM mortars and concretes. This important factor is the main difference between the behaviour of HAC blends and HAC alone, where a number of different metastable hydrates form with water which convert rapidly at higher than ambient temperatures, typically above 25”C, to form stable hydrates of increased p o r o ~ i t y . ~ However, converted Fondu was found to be no more porous than ordinary Portland Cement ( O K ) a t equal water/cement ratio.5

Hydrate formation and stability

reacts with water, the hydrate compounds bind the aggregate components together to form the strong composite concrete. Portland cements form calcium silicate hydrates (CSH) and calcium aluminate hydrates (CAH). With HAC, the major initial products are metastable calcium aluminate hydrates, CAH,, and C,AH, (with AH,), depending on temperature. These hydrates convert over a period of time to the stable hydrate hydrogarnet, C,AH,, and this process, known a s conversion, can lead to a loss in ~ t r e n g t h . ~ However, when BRECEM hydrates, gehlenite hydrate (C’ASH,) forms a s a major crystalline phase as a result of the increased silica content arising from the GGBS, thereby restricting the formation of the calcium aluminate hydrates, such as CAH,, and C,AH,, and so reducing the effects of the conversion reaction. The amount of C,ASH, formed depends on the initial mix composition. Recent hydration s t ~ d i e s ’ - ~ - ~ have shown that the conversion reactions are greatly altered in the presence of slag. The effect of slag addition on the hydration chemistry of calcium aluminates has been studied by various techniques using both pure compounds (e.g. CA and C,,A,) and commercial cements.’ Calcium aluminate hydrates are still produced, and contribute initially to the high early strength of the mixture. The long-term stability of gehlenite hydrate together with the temperature and com- positional range over which it forms are important criteria in assessing the performance of BRECEM.

6. Experimental studies in the system Ca0-A1,0,-Si0,-H20 at 5”C, 20°C and 38°C by Quillin and Majumdar, showed that gehlenite hydrate, C,ASH,, formed over a wide range

5. When cement, whether OPC or HAC,

* Cement chemistry nomenclature is a s follows:

of oxide compositions and in large amounts at compositions close to those of BRECEM mixes. With BRECEM, conversion should be less significant than in HAC where C,ASH, forms only in small quantities. The stability of gehlenite hydrate is consistent with the results of the durability studies, discussed later, which showed that concretes made with BRECEM maintain their strength over long periods of time and at a range of temperatures. However, the reaction kinetics and temperature changes during the early stages of hydration need to be considered further.,

Comparison of physical and chemical properties of BRECEM and HAC concretes

concrete products such as tiles, pipes or, indeed, in structural precast concrete units, then to ensure its safe and proper use, the long- term chemical stability of gehlenite hydrate in mortars and concretes must be established. A comprehensive programme of durability studies has been set up at BRE to investigate the robustness of BRECEM to variations in mix design and its durability in a variety of environments. The studies include the performance of mortar prisms in strong sodium and magnesium sulphate solutions, and of concrete specimens, as 100 mm cubes, stored for longer ages in water at different temperatures and in a number of aggressive sulphate, sea water and acidic water environments.

ments had been used to determine the heat output and phase composition of HAC or ‘Fondu’ cements, with and without additions of GGBS.’ Adiabatic temperature measurements were then carried out using different sized concrete specimens, from 150 mm cubesg to 1 m blocks, with cores being subsequently tested at ages between seven and 28 days and at later ages to assess strength development and hydrate formation.

Sulphate resistance of mortars

HAC + GGBS mixtures was determined, using several accelerated testing methods employing sodium and magnesium sulphate solution^.^ Use was made of 1 : 3 mortar cubes (10 mm) and flat mortar prisms (10 mm X 40 mm X

160 mm), and the results have been reported previously.’ Fig. 1 shows the poor physical appearance of mortar prisms made from Ciment Fondu after 12 months’ storage in strong Na,SO, solution, and Fig. 2 shows the excellent appearance of similar prisms made from 1 : 1 Ciment Fondu: GGBS mixtures, after 15 months in the same test solution. It should be noted that the free water/cement ratio (w/c) of the

7. If BRECEM is to be advocated for use in

8. Earlier conduction calorimetric experi-

9. The sulphate resistance of HAC and

C = CaO; A = A1,0,; S = SiO,; H = H,O. mortars for this particular accelerated test was

BRECEM: RAPID HARDENING CEMENT

at 0.6. The superior sulphate resistance of the blended cement, clearly indicated in these pho- tographs, showed that BRECEM is far more to].

where the free w/c should not exceed 0.40 in erant to higher water additions than HAC

mortars and concretes. The sulphate resistance of HAC is known to be good under strictly con- trolled conditions of w/c ratio and cement content."

soecimens a t different temoeratures Compressiue strength development of concrete

HACjCGBS mixture, using w/c ratios of 0.45 and 0.56, and kept under water a t 20°C and 38"C, are shown in Figs 3 and 4. Majumdar and Singh'showed that, while the initial strength of concrete made from the blend was only half that of the equivalent mix design HAC concrete, the strength of the slag blend increased pro- gressively up to five years at both temperatures, irrespective of w/c ratio. At the lower w/c of 0.45, up to five years, the HAC concrete kept under water a t 20°C had not shown any reduction in strength, but from 38°C

Fig. I . Appearance of mortarprisms

from HAC after (w/c = 0.6) made

storage in 4.4% Na,SO, solution f o r 12 months

10. The compressive sirengths of 100 mm the strength was reduced significantly with concrete cubes made from HAC and a 1 : 1 time, from 80 MPa after seven days to 38 MPa

Fig. 2. Appearance of mortar prisms (w /c = 0.6) made from l : l mixture of HAC and GGBS after storage in 4.4% Na,SO, solution for 15 months

95

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HAC in water, 20°C --------- 0- HAC/GGBS, in water, 38°C ,;\/-- /A

30 t I 1 I I l

28 90 180 360 Days 1 5 10 Years

Time: log scale

Fig. 3. Compressive strength of 100 mm concrete cubes made from HAC stored in water at 20°C and 38T, and from 1 :l mixture of HAC and GGBS stored at 20°C and 38"; wlc ratio 0.45

after 90 days, and increasing slightly thereafter (see Fig. 3). The use of the higher w/c ratio of 0.56 demonstrated quite dramatically the greater stability and strength that BRECEM concretes were able to sustain, for concrete mixes a t 20°C and 38°C (Fig. 4). The five-year old BRECEM specimens contained large quantities of gehlenite hydrate, and this phase

Fig. 4 . Compressive strength of 100 mm concrete cubes made from HAC stored in water at 20°C and 38T, and from l : l mixture of HAC and GGBS stored at 20°C and 38°C; w / c ratio 0.56

80

I -A-

2o t t

I

I I I l I I

7 28 90 180 360 Days 1 5 10

Time: log scale Years

appeared to be the predominant product of hydration and responsible for the more consistent performance and improved strength characteristics exhibited by BRECEM compared with HAC concretes.

Durability of concrete specimens in aggressive environments at one year

11. A series of concrete mixes containing HAC and blends of HAC and GGBS was pre- pared according to the mix design in Table 1, and 100 mm cubes, taken randomly from each mix, were placed in a number of aggressive storage environments following different pre- curing regimes. The performance of the concrete cubes was assessed at one year in terms of their visual appearance, attack ratings and retention of compressive strength by an established method of assessment used previously. Storage was in the following environments: in sulphate solutions, in spray, tidal and full immersion zones of the BRE Marine exposure site at Shoeburyness on the Thames estuary;13 in soft acid water at Butterley reservoir in south-west Yorkshire; and on the BRE exposure site at Garston. The degree of attack and strength retention will also be measured at later ages on specimens stored for two, five and 10 years.

Sulphate resistance

cured in water a t 20°C for 27 days after demoulding at 24 hours, were stored in four separate tanks of sodium and magnesium sulphate solutions containing the equivalent of 0.35% SO, and 1.5% SO, by weight of sulphate. These solutions represent classes 4 and 5 conditions of sulphate respectively as classified by BRE Digest 363.14 Using three cubes from each solution, the assessment of their sulphate resistance at one year showed clearly that, to date, both BRECEM and HAC concrete specimens had performed very well, with excellent strength retention.

Marine and acid water resistance 13. Concrete cubes, 100 mm in size and pre-

cured either in water a t 5"C, 20°C or 38"C, or in air at 20°C and 65% relative humidity (RH) for the first 27 days, after demoulding at 24 hours, were then randomly distributed and stored in different aggressive environments : marine exposure site (tidal, full immersion and spray zones); soft acid water; Garston exposure site; and in water at 20°C (as controls). The specimens (three cubes from each storage condition) were tested and assessed at an age of one year.

14. The results showed that, irrespective of pre-cure or storage situation, BRECEM concretes have, on the whole, performed very well, with generally greater than 90% strength retention compared with the water-stored control

12. Concrete cubes, 100 mm in size and pre-

BRECEM: RAPID HARDENING CEMENT

Table 1 . Concrete mix designs and wet concrete properties

Test Fresh concrete properties Concrete mix proportions conditions

Thames Valley

sand pit

Water Cement St aggregates Albans

20-10mm Slump: Wet Cement Total w/c (Slag <5 mm 10-5 mm + PC)

kg/m3 kg/m' w/c) mm density: content: (free

Seawater 60-100 2330-2370 380 0.50 1 .o 1.75 2.91 acid water (0.45)

Five-year 4-5 2380-2430 340 0.45 1 .o 2.0 3.60 compressive strength at 20" and 38°C 32-65 2380-2410 330 0.56 1 .o 2 .o 3.60

Sulphates 3.90 1.7 1 .o 25-45 2380-2420 335 0.525

specimen strengths at the same age. However, the HAC concrete cubes pre-cured a t 38°C have shown considerably reduced strength retention with the same mix design concretes, owing to the effects of the ' conversion ' reaction, with strength retentions of 40-50% compared with the 20°C water stored control specimens. It should be noted that, although these HAC concrete specimens had reduced strength, their performance in all aggressive storage conditions was good, with strength retentions greater than loo%, except for soft acid water (94%). The durability at one year was also good for HACC specimens pre-cured at 20°C and 5°C in water and stored in the same aggressive environments. Some of those pre-cured in air at 20°C and water at 5°C had reduced strength initially, as a result of conversion which was again apparent in both the spray zone and Garston outdoor exposure site situations. Dry or semi- dry conditions are known to be disadvan- tageous to HAC. Another factor to be considered is that all concretes had a w/c ratio of 0.50 (total), approximately 0.45 (free), and that this level of water was slightly higher than the 0.40 (minimum free w/c) formerly specified for HACC. BRECEM concretes, using these small specimen-size 100 mm cubes, have shown no signs of strength loss attributable to the warmer 38°C curing regime before storage in aggressive environments. This again demon- strates the greater tolerance to the effects of elevated curing temperatures for higher w/c ratio concrete mix designs, exhibited by BRECEM concretes as compared with HACC.

Adiabatic temperature rises and implications for mass concrete

is known to be an inevitable process whereby the meta-stable calcium aluminate hydrates

15. The conversion of HAC or Ciment Fondu

change to their stable form.4 This process is accelerated at temperatures above ambient, par- ticularly in mass concrete where temperatures of 80-90°C might be realized. There is a resurgence of opinion which feels that although some of the early strength is lost, an acceptable level of strength is retained which would allow HACC to be used satisfactorily for a number of non-structural or possibly even structural applications, providing that the wjc ratio is limited to a maximum of 0.40. ' v 1 '

16. Majumdar et al. reported recently the results of conduction calorimetric studies carried out on the hydration of pure calcium aluminates and on Ciment Fondu with and without slag.' They also investigated the rate of increase in the temperature of concrete cubes in a semi-adiabatic calorimeter.' As expected, both studies showed that the highest temperature rise was seen with HAC, the lowest for OPC, and BRECEM lay in between. These effects will be exaggerated in larger, mass concrete structures. However, a reduction in strength, as realized in HACC a t elevated temperatures, has been reported for HACiGGBS concretes at temperatures greater than 50"C.'5 As these temperatures are likely to be encoun- tered in practice when concretes are placed, it was decided that a special insulated mould was required in which a 1 m cube of concrete could be placed and the temperature rises monitored.

17. The adiabatic temperature rise of concrete made from a 50/50 mixture of HAC and GGBS, using a total w/c ratio of 0.55 (free w/c approximately 0.50), was measured using the metre cube mould insulated with 100 mm thick styrofoam. The concrete was poured in three layers and was compacted by means of a vibrating poker. The temperatures at the centre and at one quarter length from the edges of the concrete cube were recorded using embedded

OSBORNE

sensors. The cube was demoulded after seven days and a 100 mm core was cut through the metre cube for compressive strength determination and hydrate formation assessment. A similar exercise was carried out using HAC concrete, which was of different mix design to ensure a free w/c of approximately 0.4 as deemed necessary for HACC. The results of the compressive strength tests and X-ray diffraction data for the hydrate formation are compared in Table 2.

18. Although a direct comparison between the properties of the two concretes cannot be made, a s different mix designs and w/c ratios were used, it is possible to make a general assessment of their behaviour and performance.

HAC concrete 19. The maximum temperature of 91°C was

developed within only nine hours; however, no thermal cracking was observed on the surfaces of the metre cube. The temperature decreased very slowly over the first seven days to approximately 70"C, while the cube remained fully insulated in a near adiabatic environment, simulating a mass concrete situation. Cores taken at seven and 28 days and tested at nine days and and at about one month, had mean compressive strengths of 41 MPa and 36 MPa respectively. These strength data and the evi- dence from the hydrated compounds detected by X-ray diffraction in the crushed-up core samples, where the stable hydrates C,AH, and AH, were found, indicated that the HAC had converted fully to produce a stable concrete with a strength of about 40 MPa. This conclu- sion, which is in line with the findings of Currie and Crammond,' will need to be substantiated, and further tests will be carried out on cores taken from the metre cube at six months and one year to determine the longer term performance.

Table 2. Properties of l m concrete cubes

Code No.

390 Cement content (kg/m3)

1 : 1.75 : 2.91 Mix proportion

HAC Cement type

A 93/160

w/c ratio 0.45

Maximum temperature reached ("C) 91.2

Compressive strength (MPa) (100 mm cores) 9 days

36.0 29-32 days 41 .O

230 days Test awaited

Hydrated phases (in cores) 9 days

C3AH,, AH3 29-32 days C,AH,, AH3 -

98

A 9212.53

50/50 HAC : GGBS

1 : 2.50 : 3.50

320

0.55

58.0

19.5 21.0 24.5

BRECEM concrete 20. In comparison with the HAC concrete,

the metre cube of BRECEM concrete contained less 'cement' (320 kg/m3, with 50 : 50 by weight of HAC : GGBS compared with 390 kg/m3), more aggregate (A/C = 1 : 6 compared with 1 : 466), and had an increased total w/c ratio of 0.55 compared with 0.45. The maximum temperature attained was considerably less at 58°C compared with 91"C, but the mean compressive strength developed was surprisingly low at 20 MPa, 21 MPa and 24.5 MPa respectively when tested at nine days, about one month and a t 230 days. These early strength data indicate that the HAC component in BRECEM may have hydrated preferentially and then possibly converted as the concrete temperature exceeded 25"C, at the expense of the HAC-GGBS reaction. The formation of gehlenite hydrate and a hydrogarnet phase containing some silica from the slag with AH, is, however, encouraging, a s the presence of these hydrates suggests that the HAC-GGBS reaction to form C,ASH, has occurred to some extent. The longer term tests at later ages will be of signifi- cance in establishing whether or not the charac- teristic, gradual strength development associated with smaller sections (100 mm cubes) of BRECEM concrete' is fully realized in mass concrete. The steady increase to 24.5 MPa at 230 days is also encouraging. These are important studies to elucidate the effect of specimen size and high curing temperatures, such as 60°C and above, on the chemical and physical properties of BRECEM concrete.

Comparative cost of BRECEM and potential applications

carry out studies on the development of BRECEM lies in the assumption that it will offer a cementitious system that gives a high strength, rapid rate of gain of strength and extremely high chemical durability. Addi- tionally, although there are environmental advantages, on account of its use of industrial byproducts such as GGBS, that lead to low embodied energy and reduced carbon dioxide emissions, there have to be identifiable and marketable outlets for the application of BRECEM. Once markets have been established, there could also be substantial potential returns for the BRE or its industrial partners from the exploitation of the patent rights on the trademark BRECEM. However, if any potential application is to be successful and worthwhile, it must either be cost-effective in comparison with other existing products or hold viable prospects for any new uses.

Comparative cost of BRECEM

general basic cost comparisons between

21. The overall justification for the BRE to

22. It is possible to provide only very

BRECEM and the main existing cementitious materials involved, e.g. ordinary, rapid hardening and sulphate resisting Portland cement (OPC, RHPC and SRPC), ground granulated blastfurnace slag (GGBS) and HAC. If the Board of Trade figures for ex-factory costs per tonne of OPC and HAC are compared, it is generally seen that HAC is at least four times as expensive a s OPC, and GGBS will be about 70% of the cost of OPC. Hence, a 50/50 HAC : GGBS blend, which could be the typical combination to be used as BRECEM, is likely to cost two to three times that of OPC or OPC : GGBS blends. Where sulphate resistance is specifically required, then the cost will be approximately twice that of SRPC.

23. Potential applications may occur where the respective materials costs will be of secondary importance, owing to the specific needs of the job, e.g. for very rapid early strength development required in comrete repairs to airport runways. However, with other prospective uses, the cost of the materials will be a predominant factor, as there are cheaper materials such a s OPC, GGBS and pulverized fuel ash which could be properly and effectively used for that purpose, e.g. in precast concrete. The basic materials cost of different cements or secondary cementitious materials are all subject to variability through supply, demand, location and the particular use. The objective of the BRE durability studies, which have now reached the two-year test stage, is to assess and demonstrate the suitability of BRECEM mortars and concretes, a s compared with HAC and OPC concretes, for use in all types of struc- ture, both for non-structural and structural purposes.

Non-structural uses 24. The use of BRECEM for the repair of

concrete and for winter concreting is being assessed, as these applications offer excellent opportunities for successful utilization. The work on BRECEM as a repair material will exploit existing BRE expertise to assess its effectiveness for this specialist use. For winter concreting, where the correct balance of concrete temperatures and early strength require- ments are important, the BRE studies will cover the effect of low temperatures on the hydration of BRECEM and will involve practical tests on concrete in cold conditions.

25. The work will also assess whether or not the formation of thaumasiteI6 can be pre- vented in BRECEM mortars and concretes. Smaller section concrete pipes and roofing tiles could also arguably be considered for non- structural components.

Structural concrete

purposes (where it has its widest potential 26. If BRECEM is to be used for structural

BRECEM : RAPID HARDENING CEMENT

application), it will be necessary to establish its durability and robustness to misuse. The five- year programme to investigate the durability of BRECEM is well underway, with the eventual aim of securing its use through an Agrement Certificate or European Technical Approval. The programme has industrial sponsorship through a consortium of Lafarge Special Cements and the Cementitious Slag Manufac- turers Association.

tions for which the special properties that BRECEM concrete offer may hold advantages over other concrete components in existing markets. The possibility of building-in some components made with BRECEM to the new Cardington facility,” for comparison with similar components made using other cements, will be explored. This will enable the full-scale use of BRECEM in a structural situation to be demonstrated and monitored, e.g. as precast floor slabs. In these studies, the early strengths required for transfer of prestress and other matters, such as fire resistance, could be established. Other structural applications of BRECEM include its use in precast piles, pre- stressed concrete beams and in tanks.

28. It is with these prospective uses of BRECEM that the price of the materials becomes a more important factor in the overall equation of costs. Continued or new industrial support, towards securing collaborative research funding, will be necessary to enhance the prospective outlets of this novel cementing material.

27. There may be certain structural applica-

References 1.

2.

3.

4.

5.

6.

7.

CURRIE R. J. and CRAMMOND N. J. Assessment of existing HAC concrete construction in the UK. h o c . Instn Ciu. Engrs Structs & Bldgs, 1994, 104, Feb., 83-92. MAJUMDAR A. J. et al. Blended high-alumina cements. Proc. Int. Conf. on Advances in Cementi- tious Materials, Gaitherburg. Ceram. Trans.,

BATE S. C. C. Report on the failure of roof beams at SiT John Cuss’s Foundation and Red Coat Church of England Secondary School, Stepney. Building Research Establishment, Garston, 1974, BRE Current Paper CP58174, 18. MIDGLEY H. G. and MIDGLEY A. The conversion of high alumina cement. Mug. Concr. Res., 1975, 27, 59-77. GEORGE C. M. (MANGABHAI R. J. (ed.)). Manufacture and performance of aluminous cement: a new per- spective. Calcium aluminate cements. E. & F. N. Spon, London, 1990,181-207. MAJUMDAR A. J. et al. Hydration of calcium aluminates in the presence of granulated blastfurnace slag. Proc. Int. Symp. on Calcium Aluminate Cements, London, 1990, July, 259-271. MAIUMDAR A. J. et al. Hydration of mixtures of ‘ Ciment Fondu ’ aluminous cement and granulated blastfurnace slag. Cem. & Concr. Res., 1990,

1991, July, 16,661-678.

20,197-208.

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8. QUILLIN K. C. and MAJUMDAR A. J. Phase equi- libria in the Ca0-A1,03-Si0,-H,0 system a t 5"C, 20°C and 38°C. Paper submitted to Adv. in Cem. Res.

9. MAJUMDAR A. J. and SINGH B. Properties of some blended high-alumina cements. Cem. & Concr. Res., 1992,22, 1101-1114.

10. OSBORNE G. J. Determination of the sulphate resistance of blastfurnace slag cement using small-scale accelerated methods of test. Adv. in Cem. Res., 1989, 2, No. 5, 21-27.

11. MONTGOMERY R. G. J. et al. Calcium aluminates and their derivatives: New applications and new technologies. Proc. Int. Conf. 'Concrete 2000 ', University of Dundee, 1993, Sept., 2, 1857-1879.

12. OSBORNE G. J. The sulphate resistance of Portland and blastfurnace slag cement concretes. Proc. 2nd CANMETIACI Int. Conf. on the Durability of Concrete, Montreal, 1991, Aug., 11, SP-126, 1047- 1071.

13. OSBORNE G. J. Concrete durability studies a t the

Building Research Establishment Marine Expo- sure site, Shoeburyness. Proc. Marine Concrete '86. The Concrete Society, London, 1986, 157- 164.

14. BUILDING RESEARCH ESTABLISHMENT. Sulphate and acid resistance of concrete in the ground. BRE, Garston, 1991, July, Digest 363.

15. FENTIMAN C. H., and RASHID S. The effect of curing conditions on the hydration and strength development in Fondu: Slag. Proc. Int. Symp. on Calcium Aluminate Cements, London, 1990, July, 272-281.

16. CRAMMOND N. J. and NIXON P. J. (NAGATAKI S. et al. (eds)). Deterioration of concrete foundation piles as a result of thaumasite formation. Proc. 6th Conf. on Durability ofBuilding Materials and Components, Omiya, 1993, Oct., E. & F. N. Spon, London, 1993,295-305.

17. CARDINGTON ENGINEERING LABORATORY. Card- ington ready for use. Breview, 1992, Autumn, Issue 5 , l .

a rapid hardening cement based on high alumina cement

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