Mortars Setting

Abdelrazig et al. (1984) studied the commercial FEB SET-45 cements and mortars (Set Products Inc., Master Builders Division, Martin Marietta Corporation). Their hydration behaviour is similar to those described above. The mortars normally set in 15 minutes and hardened in 30 to 60... 

The different mortar set-ups and other test arrangements can be varied to give a higher or lower probability of ignition consequently, different safety grades for the explosives have been defined. 

There are many types of mechanical grinding equipment available ball mills, ball and mortar sets, planetary mortars, impact mills, etc. These are available in a variety of materials steels, porcelain, agate, mullite, silicon carbide, tungsten carbide and others. Prices range from 200 to about 2,000. Unfortunately, the cost increases rather markedly as one goes to the harder materials, especially the carbides. 

In a manner similar to Portland cement, the hydration of HAC can be accelerated or retarded by the use of suitable admixtures. The most common accelerators are lithium salts, which can make HAC mortars set in a few minutes and the temperature rise to the boiling point of water. Hydro-xycarboxylic acids are the most commonly used retarders. 

Bricklaying mortar is made by mixing slaked lime, Ca(OH)2, with sand and water. The mortar hardens as the mixture dries and calcium hydroxide crystallizes. Over time, however, the mortar sets to a harder solid as calcium hydroxide reacts with carbon dioxide in the air to form calcium carbonate crystals that intertwine with the sand particles. ... 

MORTAR. In laboratory tests, conventional mortars react with aluminum alloys in the same manner as cement and concrete. While the mortar is liquid, etching of aluminum alloys occurs but the reaction stops after the mortar sets. It is good engineering practice to protect the aluminum from crevice corro-... 

Cement-based mortars set chemically, they harden hydraulically by the addition of water, they bind by the reaction of the cement with water in air and even under water, and are water resistant after cming. To take into account the need for more and more short-term completion of construction, in recent years rapid construction adhesive mortar based on special cements have been developed increasingly. The joints of these adhesive mortars may already be filled up just horns after the laying of the tiles (Geiss 2006a). 

Place 50 g. of o-chloronitrobenzene and 75 g. of clean dry sand in a 250 ml. flask equipped with a mechanical stirrer. Heat the mixture in an oil or fusible metal bath to 215-225° and add, during 40 minutes, 50 g. of copper bronze or, better, of activated copper bronze (Section 11,50, 4) (1), Maintain the temperature at 215-225° for a further 90 minutes and stir continuously. Pour the hot mixture into a Pyrex beaker containing 125 g. of sand and stir until small lumps are formed if the reaction mixture is allowed to cool in the flask, it will set to a hard mass, which can only be removed by breaking the flask. Break up the small lumps by powdering in a mortar, and boil them for 10 minutes with two 400 ml. 

Specialty Refractories. Bulk refractory products include gunning, ramming, or plastic mixes, granular materials, and hydrauhc setting castables and mortars. These products are generally made from the same raw materials as their brick counterparts. 

Morta.r, Mortar, principally slaked lime and sand, sets because of the evaporation of water, the deposition of calcium hydroxide, and the absorption of water by the bricks or cement blocks, foUowed by hardening as a result of the absorption and reaction of carbon dioxide. 

Concrete, Mortar, and Plaster. Citric acid and citrate salts are used as admixtures in concrete, mortar, and plaster formulations to retard setting times and reduce the amount of water requited to make a workable mixture (172—180). The citrate ion slows the hydration of Portland cement and acts as a dispersant, reducing the viscosity of the system (181). At levels below 0.1%, citrates accelerate the setting rate while at 0.2—0.4% the set rate is retarded. High early strength and improved frost resistance have been reported when adding citrate to concrete, mortar, and plaster. 

The PLS calibration set was built mixing in an agate mortar different amounts of Mancozeb standard with kaolin, a coadjuvant usually formulated in agrochemicals. Cluster analysis was employed for sample classification and to select the adequate PLS model acording with the characteristics of the sample matrix and the presence of other components. 

Into this category come the water-based plasters, mortars, cements and concretes which set at room temperature as the result of a chemical reaction between water and a powder. Some of these have been known... 

Abdelrazig, Sharp El-Jazairi (1988, 1989) prepared a series of mortars based on a powder blend of MgO and ADP with a quartz sand filler. They were hydrated by mixing with water. A mortar I (MgO ADP silica water = 17T 12-9 70-0 12-5), with a water/solid ratio of 1 8, formed a workable paste which set in 7 minutes with evolution of ammonia. The main hydration product, struvite, was formed in appreciable amounts within 5 minutes and continued to increase. Schertelite also appeared, but only in minor amounts, within the first 5 minutes and persisted only during the first hour of the reaction. Dittmarite appeared in minor amounts after 15 minutes, and persisted. 

The addition of STPP (1-7%) acted as a retarder and increased compressive strength (mortar II). Less heat and ammonia were evolved and the cement set more slowly in 10 minutes. The paste hardened in 30 to 60 minutes. Traces of ADP persisted for 30 minutes but no STPP was detected in the reaction products. Struvite, the main hydration product, schertelite and dittmarite all appeared within 5 minutes. Struvite continued to increase in amount as the cement aged schertelite disappeared after 3 hours and dittmarite after a week. Stercorite was found only during the first 7 hours. 

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