St Astier Natural Hydraulic Limes (NHL)

Chemistry and mineralogy of the raw material

~ Manufacturing and finished products chemical and mineralogical data -
Thermocromex is produced from the burning and slaking of a pure chalky limestone with siliceous content. No additions are made. They strictly conform to the French Norm NFP 15.311 and the European Norm EN 459 classifying NHL.
~ The limestone in the St. Astier basin (approx. 40 Km²) derives from crustacean deposits (chalky limestone) infiltrated by silica but untouched by clay. Exploited for thousands of years, industrial production began in 1851. The quarries, owned by the same group from the industrial beginning, extend for 300,000 square meters (30 hectares). Tests conducted by the French government show a unique uniformity in the composition of the deposits (up to 100 m. depth).

Chemical and mineralogical analysis of the deposit:

Chemical Analysis	Loss at ignition	CaO	SiO2	MgO	Al2O3*	Fe2O3*	SO3*	Na2O*	K2O*	Others*
%	40	44	13	0.6	1.1	0.32	0	0.04	0.1	0.84

• The absence of clay infiltration and the consequent minimal presence of Al₂‚O₃, sulfates and alkalis ensure the production of hydraulic limes based almost totally on the combination of Calcium Oxide and reactive silica.

 

Corresponding Mineralogical Composition	H2O (moisture content)	CaCO3	SiO2 (soluble)	SiO2(insoluble)	MgCO3	Others (derivatives from items marked * above)
%	8	75	11	2	1	3
			Reactive/combinable	Inert/un-combinable

• The soluble silica, available to be combined with the CaO produced in the burning of the CaCO₃ determines the hydraulicity of the finished products.

The production of different types of Natural Hydraulic Limes from the same raw material deposits proves that hydraulicity depends on the amount of silica combined and not on the total amount present. The theory that hydraulicity depends on the total amount of "clay (or silica)" in the raw material is fundamentally flawed.

The production method is essentially unchanged from the one used since ancient times: limestone burned and slaked. It is therefore correct to say that Thermocromex is amongst the very few traditionally produced limes. The scientific knowledge of the manufacturer and modern quality control has, however, the favorable effect of producing reliable materials with constant performance.

The burning process: Its methods and the energy used are the determining factors in the quantity of silica that combines with Calcium Oxide (CaO) to form Calcium Silicates (CS) which produces the hydraulic performance of the finished products. Burning takes place in vertical kilns at temperatures not above 1832^oF (1,000^oC). The fuel is anthracite coal, imported from Wales due to its purity, as it produces the least residuals.
Continuous checks are made to measure the efficiency of the burning (CO₂ tests) which are essential to regulate the hydration that follows.

Hydration (slaking): The controlled hydration process is so precise that virtually no quick lime (<1%) will be present at the end. The efficiency of the slaking process is such that only a small percentage of the slaked material has to be milled to achieve the desired granulometry (0.09mm). As shown below, the amount of potentially damaging components produced is so minute that adverse reactions, leading to materials deterioration, are not possible.

* The presence of SO₃, absent in the raw material, is induced by the coal used in burning. The small level of it, however, is harmless. Higher gypsum (CaSO₄) levels due to additions as in the case of ordinary cement or some other hydraulic binders can cause damage.

C₃S can occur due to "high spots" in the furnace and also due to eutectic reactions caused by the presence of alkalis which lowers the fusion point.

 

EU Norms (EN 459 Mandatory testing program for Natural Hydraulic Limes

POWDERS
TEST	NORM	EN459 Values	St Astier Values	Frequency EU Norms	St. Astier Frequency
Fineness	EN196-6	residue by mass 0.09mm/0.2mm <15%/<5%	5-7%	daily	Daily
Free water	EN459-2	3.5<2	<2
Soundness (Expansion)	EN459-2	<2	<1	once a day	several times per day
Bulk density Kg/dm3	EN459-2	NHL3.50.5-0.9	0.61/0.65	monthly	each product batch

 

FINISHES (prepared with standard EU sand/ISO 679 @ 1:1 vol. ratio
Penetration	EN459-2	>20mm	>20mm	monthly	Weekly
		<50mm	<50mm
Setting time	EN459-2	>1h/<15h	>3h/<10h	2 per week	2 per week
Air content	EN459-2	<20	<20	monthly	monthly
Compressive	EN459-2	28 days		weekly	continuously
Strength		N/mm2
NHL3.5		3.5 to 10	3.5 to 6
SO3	EN196-2
content %		3*	0.45/0.65	monthly	continuously
*up to 7% admissible if soundness is demonstrated at 28 days of water curing
Available	EN459-2	NHL53%	15-20%	weekly	each product batch
Lime	minimum	NHL3.59%	22-26%		each product batch
	values	NHL215%	50-55%		each product batch

Other tests regularly performed by the St. Astier Research & Development Dept:
CO₂ contents after each burning to regulate slaking, Tensile strength, Elasticity moduli, Adhesion, Workability (flow table), Whiteness.

Ecological Evaluation of Lime Binders using Natural Lime

CO₂ re-absorption comparison for Thermocromex compared with similar Portland cement: Lime Finish Mixes

Carbon Dioxide deficit for 1 Cubic Meter of finish.