Cement-sand Mortar Research Articles

Experience with use of cement-sand mortar as sewer waterproofing material

Experience with use of cement-sand mortar as sewer waterproofing material

Strata Reinforcement with bolting and wire-rope systems—a comparative study

Rock bolts and wire-ropes are in extensive use for ground support in mines, tunnels and other excavations. A simple and economical method of support using scrap wire ropes, conceptually similar to a roof truss, was evolved in 1974 for use in Indian coal mines. The technique, (rope or truss), has since found wide application in coal mines in India for support of the roof and sides of roadways. The method comprises essentially the following: two holes are drilled in the roof on either side of the roadway at an inclination of 45 deg and to a depth of 1.8 M. Using a sand-cement mortar, two ends of a rope are grouted in the holes. After the grout has set, timber laggings are used to tighten the rope against the roof. For roadway spans exceeding 3.6 M, full-column grouted bolts (with an eye-hook at the bottom) are used for additional reinforcement at mid-span. The rope is passed through the eye-hook and the ends grouted over the rib line on either side. The support system has been tried out on an experimental basis over the past 6 yr in some 60 coal mines and proved to be economical and effective vis-a-vis conventional roadway support systems. From a model study to evaluate the relative reinforcement actions with bolting and wire-rope systems it was concluded that: (1) The reinforcement increased by 17% with side bolts inclined at 60 deg and extending over the support ends vis-a-vis the vertical bolt system. (2) A steel strap interconnecting the bolts was found to act as a tension member offering resistance to the movement of the bottom layer. (3) Wire rope stitching as a system proved to be more effective than the other bolting systems examined. (TRRL)

The use of calcined serpentine as a cement

Calcined serpentine rock, a magnesian silicate hydrate, when ground to cement fineness will act as a hydraulic binder. Tests on 1:3 cement sand mortars showed that the strength development was slow and low; at one year the strength was 3.3 Pa. Mineralogical analyses have shown that heating to 640°C produces a disorganised semi-amorphous material which reacts with water to form a new magnesium silicate hydrate akin to saponite which acts as the binding agent.

Methods and practice of treating horizontal construction joints when constructing concrete dams abroad

1. Treatment of the surfaces of construction joints is an expensive operation whose performance requires additional work by the concrete-placing equipment, which to some extent adversely affects the rate of concreting. 2. In recent years the surfaces of construction joints at foreign hydroprojects in the majority of cases have been treated by high-pressure (280–420 kg/cm2) water-air jets. Comparatively recently special concrete-setting retarders began to be used on foreign construction projects, thanks to which the time during which the concrete surfaces can be treated effectively by water-air jets is increased. 3. The spreading and brushing of a thin layer of sand-cement mortar onto the surface of horizontal construction joints for a long time was standard practice abroad in preparing the joints before placing the concrete in the next blocks. Investigations conducted in recent years did not confirm the superiority of a joint with an underlying layer of mortar with respect to cohesion and density over a joint on which the sand-cement mortar was not placed. In connection with this many design organizations in a number of countries and particularly in the U.S.A. do not include the placement of an underlying layer in the concreting technical specifications. This saves cement (about 2%) and reduces labor costs for preparing the blocks for concreting and increases the efficiency of concrete plants and concrete-placing equipment.

INVESTIGATION OF TIDAL PHENOMENA IN THE CLYDE ESTUARY, USING A SCALE MODEL. (INCLUDES PHOTOGRAPH).

Synopsis. The model was constructed to horizontal and vertical scales of 1 : 5,280 and 1 : 115 respectively, and the bed was finished with a layer of cement-sand mortar. Tides were generated by a displacer, moved by mechanism designed on the principle of Lord Kelvin's tide-predicting machine to reproduce the spring/neap cycle. A hump developed on the curve of the rising spring tide in the model at the same level as that on the estuary-tide, becoming more pronounced as the wave advanced upstream. Reclamation of large areas of land on the model caused little increase in range at Glasgow. Observations taken immediately after stopping the motion of the displacer indicated that the natural period of the model was 4 hours—about one-third of the tidal period. Harmonic analysis of tide curves in the estuary showed that the amplitudes of all the harmonic components increased with distance from the estuary mouth, and that the rate of increase of the third harmonic component was greater than that of the second or fourth. The pronounced hump on the tide curve at Glasgow was caused by magnification of the third harmonic. Analysis indicated that the mean water-level at Glasgow was considerably above that at Gourock.

STUDIES ON AUTOCLAVE TESTS OF VARIOUS CEMENTS, II

The author, in continuing the previous study (This Journal, 1938, Vol. 38, No. 584, p. 397-p. 403), studied further on the autoclave test for soundness and expansion or contraction of cement or cement-sand mortar. This testing method was applied on various kinds of Portland cement and mixed Portland cement for various purposes, i.e., (1) Testing expansion or contraction, (2) Bending strength, and (3) Compressive strength from the same test pieces by using 4×4×16cm prismatic test pieces of plastic mortar, which results are briefly abstracted from the original Japanese communication, as following:(1) Cement samples were selected for studying on the value of autoclave test, especially for testing on the relation between the soundness and chemical compositions of various cements. Three samples of common Portland cement, three of low-heat or modified Portland cement, three of high iron oxide Portland cement, one of blast furnace cement, and five of high silica mixed Portland cement, so that totally fifteen samples of various kinds of cement were selected for the present study.(2) These cement samples were first compared their chemical compsiotions and various physical properties. The strength tests were also carried out in two ways, (1) the dry or non-plastic mortar of 1:3-cement and standard sand for Portland and blast furnace cements (JES 28 and 29) of Japanese Engineering Standards, and (2) the wet or plastic mortar of 1:2-or 1:1-cement and fine sand.(3) Beam test pieces (4×4×16cm) ot wet of plastic 1:2-cement and fine sand mortar were treated, after seven days common water curing, in hot water under steam pressure (5kg/cm2 and about 152-153°C or 30kg/cm2 and about 227-228°C) in autoclave for two hours, and measured the expansion or contraction after cooling in water of room temperature and atmosperi pressure. The results were sufficient to make clear the differences between various cements, especially the unsoundness of high iron oxide containing special Portlant and soundness of high silica containing mixed Portland cement by mixing about 30% of proper admixture containing large amount of soluble silica.(4) After this measurement of expansion, the beam test pieces were tested on their bending strength or modulus of rupture and then compressive strength, and these results were compared with those obtained in the above section (2) by the common curing in water of room temperature and atmospheric pressure. These comparisons are useful to discuss various mixed Portland cements being better than special Portland cements of high iron oxide or silica content.(5) Neat cement paste was tested by the LeChatelier's calliper method curing in autoclave as above mentioned and the increase of opening of calliper was compared to discuss various samples of mixed Portland cement being better than simple Portland cements containing large amount of iron oxide or silica.