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Technical Paper 

Reference : TP-GB-RE-LAF-090 

Page : 1/9 

A New Calcium Aluminate Cement resistant to Ageing 

C. Parr, H. Fryda, J. Mahiaoui, E. Larnaudie, E. Charpentier, M. Lievin. 

Kerneos SA, Paris, France 

Presented at Alafar Conference, Lima, Peru, December 2010 

Kerneos 

8, Rue des Graviers - 92521 Neuilly sur Seine Cedex, France 

Tel. : +33 1 46 37 90 00 - Fax : +33 1 46 37 92 00



Page : 2/9 

1 Introduction 

A key area for improvement of the reliability 

of deflocculated dense low calcium content 

castables (LCC) would be to increase their 

resistance to ageing and offer a much longer 

shelf-life. This would mean predictable placing 

properties irrespective of the storage time of 

the dry mix. ‘Ageing’ is a generic name used 

to describe interactions between a cement or a 

castable and the atmosphere, and the impact 

this interaction has on the cement reactivity 

and the castable properties as a function of dry 

mix storage time. Ageing manifests itself as a 

change in placing properties such as delayed 

hardening and demoulding times. Two steps 

can be described, namely, the ageing of the 

calcium aluminate cement (CAC) when stored 

alone and the ageing after the CAC has been 

introduced into the dry castable mix. Previous 

studies [1,2,3] have shown that ageing of CAC in 

both steps, leads to a weight increase which 

can be characterised by an increase in the of 

Loss on Ignition (LOI), but, depending on the 

period of ageing, the impact on the reactivity 

can be quite the opposite. The first period is a 

surface pick up of H 2 

O and CO 2 

which leads 

to a delay of dissolution of CAC, working time 

and demoulding time. The second period is 

characterised by a decrease of working time 

and the precipitation of hydrates. The presence 

of H 2 

O and CO 2 

can be due to residual moisture 

in the dry mix raw materials (CAC, alumina, 

additives, fume silica, aggregates etc.), humidity 

trapped in the bag during packing, or through 

penetration through the packaging materials. 

Thus, ageing is not just confined to a problem of 

packaging of either the cement alone nor the dry 

mix. Real benefits could be offered to the users 

through the development of ‘time stable’ CAC 

products. When used in LCC products, these 

CAC’s would provide more stable properties 

during storage and a longer shelf-life. 

The development of a clearer understanding 

of the underlying mechanisms has led to the 

development of a new calcium aluminate 

cement. The new cement is much more resistant 

to ageing and offers an intrinsic solution in 

providing predictable placing properties for 

LCC’s, and consequently extends the shelf-life. 

This paper presents results and analysis of 

different ageing experiments performed under 

different conservation and climatic conditions, 

as well as different formulations. Different 

testing conditions demonstrate the improved 

resistance to ageing that the new product can 

offer. 

2 Experimental procedure 

2.1 Material Details 

Two calcium aluminate binders have been 

used. A commercial reference product, 

Secar ® 71, based on 70% alumina (code CAC 

70) has been compared to a development 

product, PP134. The chemical, mineralogical 

and physical properties of these two binders 

are shown in Table 1. CAC 70 has a mineralogy 

based upon calcium monoaluminate (CA) and 

calcium dialuminate (CA 2 

). PP134 is a new 

calcium aluminate cement produced through a 

specific processing step which yields a similar 

chemistry and mineralogy. The objective is to 

directly substitute the PP134 for the reference 

CAC 70 in a deflocculated LCC. PP134 has 

been designed to resist moisture and CO 2 

pick 

up from the atmosphere during storage of either 

the cement alone or within a dry mix, and yet, 

to retain the normal hydraulic activity when 

water is added as the first step of the castable 

processing and installation. 

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Table 1 : Characteristics of the calcium 

aluminate cements 

Units 

CAC 70 

Typical analysis 

PP134 

Typical analysis 

Al 2 

O 3 

% 68.5 – 69.0 68.5 – 69.0 

CaO % 29.5 – 30.5 29.5 – 30.5 

SiO 2 

%



Page : 4/9 

3 Experimental results and 

discussions 

Figure 1 illustrates the typical impact of ageing 

on the hardening profile of the LCC1 castables 

as measured by the ultrasonic velocity over 

time. 

Working time (mins) 

600 

500 

400 

300 

200 

100 

5000 

0 

Time zero 2m CAC 4m CAC Time zero 2m LCC 4m LCC 

Ultrasound velocity (m/s) 

4000 

3000 

2000 

1000 

Ageing 7 days in thin layer at 

20°C and 70% r. h.. 

0 

0 60 120 180 240 300 360 420 480 540 600 660 720 780 

Time (min) 

Fig. 1 : Effect of artificial ageing of LCC1 

with CAC 70 on the ultrasonic profile. 

The whole castable dry mix was spread in a 

thin layer and exposed to 70% r.h. at 20°C for 

7 days. The ultrasonic velocity curve with time 

is typical of a LCC with silica fume and Na-TPP, 

and is characterised by two steps. The first step 

is due to CAC dissolution / castable flocculation 

and corresponds to the working time with about 

5 MPa in compressive strength. The second 

step is the massive precipitation of hydrates 

leading to real hardening, with compressive 

strength development above 10 MPa. Ageing 

typically leads to a delay of the first step, but 

the time between the first and second steps 

remains constant. This can be seen in Figure 

1 as the curve of the aged product has been 

shifted to the right but maintains the same 

profile. Other properties like water demand, 

24h, 110°C or fired strengths, porosity etc. are 

not impacted by ageing, as long as the water 

addition remains the same. 

Fig. 2 : Effect of artificial ageing of LCC1 

with CAC 70 on the working time. 

The effect of the age of the CAC (from the 

packing date) on the LCC working time has 

been evaluated. Samples of CAC 70 were 

taken and stored in sealed paper bags exposed 

to 70% r.h. at 20°C for 4 months. Bags were 

opened at 2 and 4 month intervals, the CAC 70 

mixed into a freshly batched LCC1 formula and 

the working time evaluated. Similarly, the same 

CAC 70 was taken and batched into the LCC1 

dry mix and the whole dry mix was placed in 

sealed paper bags and stored for 4 months. 

The LCC1 dry mix was tested and the placing 

properties were evaluated at 2 and 4 months. 

The results are shown in Figure 2. The left 

hand graph shows the evolution of the working 

time of the LCC1 castable when the CAC 70 of 

different ages is placed in a fresh dry mix. The 

reference working time (60 mins) is measured 

at the time that the samples of CAC 70 were 

drawn from storage. The right hand graph 

shows the ageing of the whole mix (prepared 

using fresh CAC 70) and the whole dry mix was 

then aged. At both 2 and 4 month intervals, the 

working time is around 1.5 times longer in the 

case of whole dry mix ageing relative to using a 

system where the cement has been aged alone. 

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The implications are that even with a “fresh” 

or well preserved CAC, ageing will still occur 

once the cement is placed in a dry mix where 

there is either residual moisture from the other 

components and / or exchange of moisture with 

the environment. 

With this in mind, further tests were carried out 

comparing the reference product (CAC 70) with 

the development product PP134 via simulated 

ageing of the whole mix. In other words “fresh” 

samples were placed in the dry mix inside sealed 

bags which were then placed in an environment 

of 70% r.h. at 20°C for periods up to 12 months. 

Vibration Flow (%) 

140 

120 

100 

80 

Time zero 

CAC 70 2 months 

PP134 2 months 

60 

PTT 800 mins 

40 PTT 

370 

PTT 475 mins 

20 mins 

0 

0 50 100 150 200 250 300 350 400 

Time (mins) 

Fig. 3 : Effect of artificial ageing on the 

vibration flow. 

Both the reference CAC 70 and the new PP134 

product (Figure 3) display the same vibration 

flow decay at time zero, i.e. just after dry mix 

batching. After the dry mix has been stored for 2 

months, the flow profile of CAC 70 is significantly 

extended, as is the exothermic profile (PTT) 

relative to the starting point at time zero. 

The impact of ageing conditions on castable 

working time is shown in Figure 4. In both 

cases, a significant extension of the working 

time is observed relative to the improved shelflife 

of the product. The PP134 shows a small 

initial evolution between 0 and 2 months, and 

then remains stable under the environmental 

conditions of the test. An explanation for the 

lengthening and then decreasing working time 

of CAC 70 has been proposed in [1] and it has 

been suggested that the presence of hydrates 

accelerate the nucleation. However, the working 

time remains extended relative to time zero. 

The hardening profile has been determined 

using an ultrasonic technique and the resulting 

curves are shown in Figure 5 for the reference 

CAC 70 and Figure 4 for PP134. The first 

increase in ultrasonic velocity is associated with 

the end of working time and the transition from 

a liquid to a solid. 

Working time (min) 

450 

400 

350 

300 

250 

200 

150 

100 

50 

0 

CAC 70 

PP134 

0 2 4 8 10 

Ageing time (months) 


working time. 

The shelf life stable calcium aluminate, PP134, 

shows a flow decay comparable with the initial 

profile and the extension of the exothermic 

profile is limited. 

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The second increase is associated with a gain 

in mechanical strength as the hydration process 

develops to form hydrates. In the case of the 

reference, CAC 70, an initial shift in the hardening 

profile is noted after only two months storage, with 

the ageing of the whole mix being more affected 

than the case of ageing the cement alone. A 

further extension is noted after 4 months. At this 

time, there is also a change to the shape of the 

curve indicating a slower hardening kinetic. This 

is particularly noticeable in the case of 4 months 

ageing of the whole castable mix. In practical 

terms, this would translate into an extension of 

400 to 500 minutes in the demoulding time. The 

improved time stable development product is 

able to maintain a very similar hardening profile, 

independent of the ageing conditions, and the 

initial rise is centred around 200 mins with the 

second increase at 500 mins. There is an initial 

shift from time zero i.e. wet mixing straight after 

batching and the first evaluation at 2 months, 

but thereafter the hardening profile remains 

remarkably constant. 

These profiles have been confirmed via the 

measurement of early age mechanical strength 

at 6 hours from casting after ageing at 20°C and 

70% r.h. of the whole dry mix (castable stored 

in paper sacks for up to 12 months after dry 

batching). Hardening becomes so extended 

in the model LCC1 system prepared with the 

reference CAC 70 after just two months that 

6 hour strengths can no longer be measured. 

In contrast, PP134 delivers consistent 6 hour 

strengths even after ageing for 12 months. 

There is a slight decrease from the initial values 

of 8 to 10 MPa but then the strength remains 

stable around 6 MPa. Therefore, the physical 

effects of ageing can be seen to be an extension 

of the working time (longer flow period), 

slower hardening and a delayed acquisition of 

mechanical resistance. The PP134, offering 

an intrinsic improvement to shelf-life, is able to 

ensure much more stable placing and hardening 

properties over the ageing period. 

12 

Velocity m/s 

5000 

4000 

3000 

2000 

Ref CAC 70 

2m -PP134 

4m -PP134 

4m -CAC 70 

2m -CAC 70 

CCS 6 hours (MPa) 

10 

8 

6 

4 

2 

CAC 70 PP 134 

1000 

0 

0 1 2 4 8 10 12 

0 

0 200 400 600 800 1000 

Time (min) 


ultrasonic profile. 

Months of ageing 

Fig. 6 : Effect of artificial ageing on the early 

strength development of LCC1. 

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Properties of both CAC types were compared 

in a conventional castable to demonstrate that 

they have equivalent behaviour in terms of a 

hydraulic binder, and that the development 

product PP134 will deliver equivalent installed 

characteristics to the reference system. 8% 

water was used in both cases and the tests 

were performed at 20°C with “freshly” batched 

castable. The results for conventional castable 

are shown in Table 3 and confirm that both 

CAC’s behave in a similar way when applied to 

classical refractory systems. 

Table 3 : Conventional castables 

Units CAC 70 PP134 

Flow at t0 % 110 105 

CCS after 24 MPa 67.1 70.3 

CCS after 110°C MPa 97.1 101.3 

CCS after 600°C MPa 93.9 74.7 

CCS after 1350°C MPa 50.8 48.0 

CCS after 1550°C MPa 48.3 41.0 

BD after 110°C g/cm 3 2.88 2.88 

BD after 600°C g/cm 3 2.78 2.77 

BD after 1100°C g/cm 3 2.74 2.71 

BD after 1350°C g/cm 3 2.73 2.72 

BD after 1550°C g/cm 3 2.73 2.73 

AP after 110°C % 14.9 14.6 

AP after 600°C % 15.5 17.0 

AP after 1100°C % 23.5 22.6 

AP after 1350°C % 22.4 22.3 

AP after 1550°C % 23.4 23.1 

PLC to 600°C % -0.09 -0.09 

PLC to 1100°C % -0.07 0.30 

PLC to 1350°C % -0.17 0.05 

PLC to 1550°C % -0.08 -0.06 

The physical properties as measured by 

compressive strength, bulk density, apparent 

porosity and permanent linear change are 

similar for both CAC 70 and PP134. 

The evolution of LOI has been followed over 

a period of ageing (sealed bags 70% r.h. and 

20°C) for the calcium aluminate alone to give 

a confirmation that the effects observed in 

terms of LCC behaviour are linked to the same 

mechanisms as reported in [1] . It can clearly be 

seen (Figure 7) that the PP134 is much more 

resistant to LOI gain than the reference CAC 70. 

An initial increase of around 0.1% is observed 

for the first few days and thereafter the value 

remains constant. In comparison, the reference 

product CAC 70 shows an almost exponential 

growth in LOI over the 10 months. Coherent 

with the explanations reported in [1] , lumps were 

found in the CAC 70 after 10 months of ageing. 

(It should be pointed out that this is a laboratory 

evaluation. Under standard industrial packing 

conditions, with the additional protection of 

shrinkwrap layers, the product remains stable 

over 12 months.) This is linked to the second 

period of ageing characterised by a decrease of 

working time and the precipitation of hydrates. 

The change in LOI illustrates the intrinsic 

protection afforded by the development product. 

Kerneos 


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Page : 8/9 

LOI (%) 

2.5 

2 

1.5 

1 

0.5 

0 

PP134 

CAC 70 

0 2 4 6 8 10 12 

Ageing time (months) 

Fig. 7 : Moisture pick-up as a function of 

ageing time for the two calcium aluminate 

cements. 

A further evaluation of the intrinsic ageing 

protection afforded by the time stable PP134 is 

illustrated in Figure 8. Samples of each cement 

type were exposed in a thin layer to 100% 

relative humidity at 20°C. Due to the extreme 

nature of this test, samples were only exposed 

for up to 24 hours. Under these conditions, the 

ageing is very quick. 

As can be seen from Figure 8, when the cement 

is placed in a ‘freshly’ mixed castable the working 

time is extended to more than 300 minutes 

after only 8 hours of ageing. Additional ageing 

results in a reduction of the working time to a 

value shorter than the initial value (i.e. before 

exposure to a high humidity). The LOI at 2.54% 

is indicative of hydrates being formed. This is the 

same phenomenon that is previously described 

in that extreme ageing leads to formation of 

hydrates and reduction of working time. 

Fig. 8 : Working time and LOI as a function 

of ageing at 100% r.h. 

This is in sharp contrast to the results for the 

development product shown on the right hand 

side of Figure 8. Under these extreme conditions, 

there is a gradual and progressive increase 

in working time to 156 minutes after 24 hours. 

However, the LOI increase remains limited 

to 1.3%. This shows the intrinsic protection 

afforded by the processing of PP134 which 

limits the destruction of the calcium aluminate 

hydraulic properties even at 100% r.h. 

Kerneos 


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Page : 9/9 

4 Conclusions 

The effect of ageing has been simulated 

through accelerated ‘artificial’ ageing tests and 

these have shown the dramatic changes that 

can occur to castable placing and hardening 

properties. From a practical point of view, this 

will result in variability and unpredictability 

on site depending on the freshness of the dry 

mix castable. The demoulding times would be 

difficult to predict depending upon the storage 

history of the castable. The observed effects 

occur irrespective of storage time and storage 

conditions of the CAC alone. 

Through the specific processing of a new 

calcium aluminate, development product 

PP134, is able to offer robust placing properties, 

resistant to ageing effects, irrespective of 

whether the cement is stored alone or the whole 

dry mix is aged. Once mixed with water as part 

of a dry LCC mix, the reactivity of the PP134 

as a hydraulic binder is similar to the reference 

system and no major differences are seen in 

either placing or placed properties. This should 

provide value to users in terms of both additional 

storage stability of the cement alone and, more 

importantly, a much more time stable dry mix 

which would lead to less site problems linked to 

the effects of castable ageing. 

6 References 

[1] Fryda H, Mahiaoui J, Larnaudie E, 

Charpentier E, Lievin M, Parr C. A new 

insight into the characterization of ageing 

and mechanisms that determine the shelf 

life of low cement castables. UNITECR 

2009, Salvador, Brazil. 

[2] Parr C, Revais C, Bunt N, Jones D, Bennet 

M. Ageing of Low Cement Castables. 

UNITECR 1997, New Orleans, USA: 81- 89. 

[3] Mathieu A, Bayoux JP, Vialle M. Ageing of 

Aluminous Cement in LCC. UNITECR 1995, 

Kyoto, Japan: 451 – 455. 

[4] Alt C, Wong L, Parr C. Measuring castable 

rheology by exothermic profile. Refractories 

applications; 8 (2): 15-18. 

[5] Simonin F, Wöhrmeyer C, Parr C. A new 

method for assessing Calcium Aluminate 

Cements. UNITECR 2005, Orlando, USA. 

5 Acknowledgements 

The authors would like to thank all the technicians 

and engineers at the Kerneos Research Centre 

for their excellent support during this study & 

associated development projects. 

Kerneos 


Tel. : +33 1 46 37 90 00 - Fax : +33 1 46 37 92 00

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