Observations on the experiments of Table No. LXVI. 1st. Within the limits of the experiments, whatever was the mode of slaking, or the kind of lime, the mortar was the stronger as the quantity of sand was less. The lime being measured in paste, the proportions were 1 of lime to 1 of sand; 1 of lime to 2 of sand; 1 to 3, and 1 to 4 of sand. In all the corresponding trials of the table, 1 lime in paste, to 1 sand, gave the strongest mortar in 35 cases of tenacity, and in 13 cases of hardness. 1 lime in paste, to 2 sand, gave the strongest mortar in 3 cases of tenacity, and in 1 case of hardness. 1 lime in paste, to 3 sand, gave the strongest mortar in 2 cases of tenacity, and in 2 cases of hardness. 1 lime in paste, to 4 sand, gave the strongest mortar in 0 cases of tenacity, and in 1 case of hardness. 2d. Slaking by DROWNING, or using a large quantity of water in the process of slaking, affords weaker mortar than slaking by SPRINKLING. In 24 corresponding cases of the table--The quantity and quality of the materials being alike: and there being no other difference than in the modes of slaking the lime.* Lime slaked by SPRINKLING, gave the best mortar in 22 cases of tenacity, and in 24 cases of hardness. Lime slaked by DROWNING, gave the best mortar in 2 cases of tenacity, and in O case of hardness. The average strength in all the 24 cases in which the lime was slaked by drowning was, as to tenacity, 23.79 lbs., and as to hardness, 187.00 lbs. While the average strength in all the 24 cases in which the lime was slaked by sprinkling was, as to tenacity, 38.63 lbs., and as to hardness 417.33 lbs. The relative tenacity then is as 1 to 1.62; and the relative hardness as 1 to 2.23. 3d. The experiments with air SLAKED LIME, were too few to be decisivebut the results were unfavourable to that mode of slaking. Average strength of the mortar made of air-slaked lime as to tenacity 20.80 lbs., and as to hardness 202.18 lbs. Average strength of the corresponding mortars made of lime slaked by drowning, as to tenacity 27.10 lbs., and as to hardness 207.50 lbs. Average strength of the corresponding mortars made of lime slaked by sprinkling, as to tenacity 46.70 lbs., and as to hardness 533.83 lbs. 4th. The mortars were very materially stronger at the end of 4 years and 5 months, than at the end of the first half year. Of the 26 mortars which enter into this comparison, the average strength at the end of 6 months was, as to tenacity, 22.54 lbs., and as to hardness 166.33 lbs., and at the end of 4 years and 5 months it was, as to tenacity, 35.45 lbs., and as to hardness 367.37 lbs. The relative tenacities being as 1 to 1.57, and hardness as 1 to 1.97 lbs. 5th. Brick dust, or the dust of burnt clay, improves the quality of mortars both as to tenacity and hardness. 6th. Hydraulic cement added, even in small quantities, to mortars, improves their quality sensibly. * Except in their being two different burnings of Fort Adams lime 7th. The tenacity of mortars seems to have been increased by using dry bricks, and making the mortar a little more fluid than usual. But the hardness of the mortars was rather the greatest when WET BRICKS were used. In 21 corresponding instances, wet bricks and mortar of common consistency gave the best results, as to tenacity, in 5 instances; and, as to hardness, in 12 instances. Dry brick and mortar more fluid, gave the best results as to tenacity in 16 instances; and as to hardness, in 9 instances. Table No. LXVII. Trials in December, 1836, of mortars made in December, 1835. The results show the weights in pounds required to break prisms of mortar 2 inches square, 6 inches long and 4 inches in the clear between the supports. It results from this table, and from the tables from which it has been abridged, 1st. That in mortars of cement and sand (no lime) the strength is generally greater as the quantity of sand is less. In SS comparisons, 12 exceptions. 2nd. That in mortars of sand, cement and lime-the lime remaining the same in quantity, the mortars were stronger as the quantity of sand was less in proportion to the cement. In 57 comparisons, 10 exceptions. 3rd. That in mortars of cement, sand and lime-the quantities of cement and sand being the same-the mortars were stronger as the quantities of lime were less. In 52 comparisons, 15 exceptions. 4th. That mortars made of cement and sand were materially stronger when the least possible quantity of water was used, than when the mortars were made thin. In 14 cases, 1 exception. 5th. That mortars made of cement and sand with the least possible quantity of water, were stronger when kept in a damp place, than when kept in a dry In 7 comparisons, 1 exception. The experiments did not prove this to be true with reference to mortars made thin. These results were afforded by the experiments but are not included in the above table. one. 6th. That in mixtures of lime and sand in various proportions, the mortar was generally stronger as the lime was slaked with less water. The average strength of several trials with 0.30 of water being represented by 80-with .40 of water, it was 98--with .60 of water, it was 72— with .80 of water, it was 60, and with 1.00 of water, it was 57. These results were afforded by the experiments, though not included in the table. 7th. That mortars of lime and sand are materially improved by the addition of calcined clay, but not so much as by the addition of cement A. 8th. That sand freed from dust by washing and then pounded fine, gives much better mortars, than a sand composed of particles of every size from dust (no dirt) up to grains of an inch diameter. In 21 comparisons, 2 exceptions. 9th. Many experiments were made to ascertain whether of two cements of the same manufactory, the difference being, probably, only difference of age, that cement which sets the quickest under water will give the strongest mortars in the air after a considerable lapse of time. The results leave the matter in doubt. The quick cement sometimes giving stronger mortars, and sometimes weaker. 10th. Of lime kept for three months after being slaked, before being made into mortar-the lime slaked into powder by sprinkling one-third of its bulk of water, gave the strongest mortar--represented by 250 lbs.; the lime slaked into cream gave the next strongest mortar-represented by 210 lbs., and the lime slake spontaneously during three months, the weakest mortar, represented by 202 lbs. All these mortars being much inferior to that made of the same lime which had been carefully preserved from slaking by being sealed hermetically in a jar-this last mortar being represented by 364 lbs. It must be remarked here that this result is very extraordinary for fat lime and sand; and it is probable this particular barrel of lime was somewhat hydraulic. 11th. Mortars of cement and sand in which bitter-water alone was mixed (Bitter-water being the mother water after the separation of muriate of soda from sea water,) were weaker than those in which water, or a mixture of equal parts of water and bitter-water, was used. But a mixture of equal parts of water and bitter-water gave much better mortar than water alone the strongest composition we had, being cement 13, sand 1, and equal parts of water and bitter-water. In 8 comparisons, 2 exceptions. www |