Synopsis The influence of the curing temperature on the compressive strength of cylindrical specimens of soil-cement has been studied at ages up to 3 months. Five soils—a clay, a silty clay, two sands and a gravel—were used, being stabilized with 10 per cent of ordinary Portland cement (15 per cent for the clay). Methods have been developed for coating or enclosing the specimens to prevent changes in their moisture contents during curing at temperatures up to 140°C. The following conclusions have been deduced:— (1) For a soil-cement road base constructed in the spring the strength during the first three months will be some 50 to 100 per cent greater than if the base were constructed in the autumn. (2) If compressive strength is taken as the sole criterion of soil-cement, less cement should be needed to stabilize a soil under tropical than under temperate conditions. (3) Soil-cement will harden in cold weather provided that the temperature is not below 0°C. (4) The 7-day strength of soil-cement changes by 2·O-2·5 per cent with each degree centigrade change in the curing temperature when the latter is near 25°C. (5) With the cohesive soils, the 7-day strength at 25°C. was approximately obtained in 1 day when the curing temperature was raised to 45°C. but only after 26 days when it was reduced to O°C. (6) The nature of the strength/age relationships obtained with the cohesive soils suggests that at temperatures up to 45°C one mechanism of hardening is involved; and that this is accelerated by increased temperature. At 60°C and 100°C variable results were obtained with the silty clay, consistent with more than one type of mechanism of hardening. L'influence de la température de la prise sur la résistance à la compression de spécimens cylindriques de mélange sol-ciment a été étudiée à des âges de mélanges allant jusqu'à trois mois. Cinq sols (un d'argile, un d'rgile limoneuse, deux de sable et un de gravier) ont été utilisés. I1s furent stabilisés avec 10 pour cent de ciment ordinaire Portland (15 per cent pour l'argile). On a mis au point certaines méthodes de revêtement ou d'enrobage des spécimens afin d'empêcher toute modification de leur teneur en eau durant la prise à des températures allant jusqu'à 140°C. On en est arrivé aux conclusions suivantes: (1) Pour une fondation de route sol-ciment construite au printemps, la résistance sera d'environ 50 à 100 pour cent plus grande. durant les trois premiers mois, que si la base avait été construite en automne. (2) Si la résistance à la compression est prise comme seul critère du mélange sol-ciment, il faudra moins de ciment pour stabiliser un sol dans un climat tropical que dans un climat tempéré (3) Le mélange sol-ciment durcira par temps froid à condition que la temperature ne descende pas en-dessous de 0°C. (4) La résistance de 7 jours du sol-ciment change de 2 à 2,5 pour cent par degré centrigrade de variation de la température de la prise, lorsque celle-ci est proche de 25°C. (5) Avec des sols cohérents, cette résistance de 7 jours a 25°C fut obtenue en 1 jour environ, lorsque la température fut élevée à 45°C, mais seulement après 26 jours, lorsqu'elle fut réduite à 0°C. (6) La nature des rapports résistance/âge obtenus avec des sols cohérents suggète qu'à des témperatures allant jusqu'à 45°C un processus de durissement a lieu et qu'il est accéléré par tout accroîssement de température. A 60°C et à 100°C. des résultats variables furent obtenus avec de l'argile limoneuse, correspondant à plus d'un seul type de processus de durcissement.
Summary: The relationships between unconfined compressive strength and age up to 28 days have been determined for soil-cement specimens made with a sand, a silty clay and a clay, stabilized with four different cements. A comparison has also been made of the effects on compressive strength of coating test specimens with wax and of placing them in a humid atmosphere during the curing period. High-alumina cement was found to give the highest strength after 24 hours, wirh all three soils, but afier 28 days it gave lower strengths than the other cements. Rapid-hardening cement was found to give strengths 20-40 lb per sq. in. greater than normal Portland cement with the two cohesive soils, while super-rapid-hardening cement generally gave strengths about 40 lb per sq. in. lower than those obtained with the other two Portland-type cements. The setting of normal Portland and rapid-hardening cement mixed with the sand was retarded for seven days, due to an organic impurity, but the setting of high-alumina cement was not affected. The addition of lime, or calcium chloride (e.g. in super-rapid-hardening cement) was found to reduce the retardation, the latter being the most effective. The action of calcium chloride in this respect was confirmed with three other soils containing deleterious organic matter. Coating test specimens with paraffin wax during the curing period was found to result in considerably smaller differences in moisture content among similar specimens in a batch than was obtained by storage in a humid atmosphere. This was accompanied by a reduction in the differences in the unconfined compressive strength of specimens only in the case of the sand-cement. The average limits of error of the mean compressive strengths based on ten independent measurements were calculated to be between ±10 and ±20 lb per sq. in. for strengths ranging between 200 and 400 lb per sq. in.
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