Technology

uses of low-cost construction materials outlined

Cairo's Youssef, Lehigh's Fang, and Oscar Hidalgo, director of Colombia's Bamboo Research Center (left to right), examine lattice made of bamboo

Symposium at Lehigh

examined potential of wastes

and plentiful natural material

such as fly ash, sulfur, rice

husks, crushed glass, bamboo

Fly ash; sulfur; shredded rubber; tunnel boring machine "muck"; crushed glass; date palm mid-ribs; bamboo; rice husk. Some of these materials are wastes. Some are plentiful natural substances in par­ticular localities. All are potential low-cost construction materials.

Getting a handle on just how good that potential might be was one aim of a three-day international symposium held early this month in Bethlehem, Pa. Sponsored by Lehigh University, the symposium on new horizons in construc­tion materials drew some 100 scientists and engineers from the U.S. and 11 for­eign countries.

The wide variety of unusual materials under study for possible construction use is a response by construction materials researchers to several current or foreseen problems. Among them are an increasing demand for building materials; decreasing supply of raw materials such as cement, aggregate, and reinforcing steel; and ac­celerating building costs.

In some cases the focus is on use of waste materials such as the fly ash, shredded rubber, and mining waste. In other cases, especially in developing countries, the emphasis is on the low-cost natural materials such as bamboo and rice husk.

A sampling of work discussed at the Lehigh conference gives a good indication of where much research on construction materials is heading:

• Fly ash as a structural fill and in construction of pavements.

• Sulfur as a partial replacement for asphalt in pavements.

• Shredded rubber as a filler in con­crete.

• Tunnel boring machine muck as a concrete aggregate.

• Crushed glass as an aggregate re­placement.

• Date palm mid-ribs as a substitute for steel reinforcement in structural con­crete.

• Bamboo as a reinforcing material for concrete.

• Rice husk in particle boards and rice husk ash as a cementitious material.

Fly ash is a good example of a waste

material begging to be used. Rutgers University civil engineer Yong S. Chae noted at the Lehigh conference that up to 50 million tons of fly ash are being gen­erated in the U.S. annually and only 12 to 14% of it is being used. Chae and co­workers have been studying the use of New Jersey fly ash as structural fill.

Chae notes that the engineering prop­erties and characteristics of fly ash vary widely from area to area, depending not only on the particular coal burned but also on the combustion process used. For ex­ample, in the New Jersey fly ash studied by Chae, silica, alumina, and iron oxide make up 91% by weight of the material— greater, Chae notes, than for typical fly ash produced in other regions. Also, he finds, the New Jersey fly ash is a pre­dominantly coarse silt-sized material and is much more uniform in gradation than others.

Chae studied various engineering properties of the New Jersey fly ash, in­cluding compaction and density proper­ties, strength, permeability and drainage, and compressibility. He finds that with proper placement and compaction, the fly ash is well suited as an adequate struc­tural fill. Placement by wet mixing along with electroosmotic stabilization, he says, seems feasible as an effective way to con­struct a load-bearing fill, and use of vi­bratory compaction also appears prom­ising.

Echoing Chae, James F. Meyers, of GAI Consultants Inc., says that fly ash should be considered a "by-product resource" rather than waste. Working with the Na­tional Ash Association, GAI has devel­oped a publication, "Guide for the Design and Construction of Cement-stabilized

Fly Ash Pavements." Fly ash, Meyers notes, is a pozzolanic material, and thus, adding small amounts of lime or cement and water can result in rapid and signifi­cant strength development.

A demonstration project at the Harri­son Power Station in Heywood, W.Va., points up the potential of cement-stabi­lized fly ash as a paving material. A parking lot base course (with bituminous wear surface) was constructed there in September 1975, with about 10,000 square yards of pavement using 3800 tons of fly ash. It was constructed by a standard paving crew using conventional equip­ment and at an economically competitive price. The demonstration pavement suf­fered no loss of strength during its first winter—a "very satisfactory perfor­mance," Meyers says.

Pavement for highways represents a possible major use for sulfur. And, indeed, there has been an increase in research activities toward this end, notes Dr. Dan Saylak, professor of civil engineering at Texas A&M University. Sulfur is ex­pected to be abundant in the future as a result of fuel desulfurization. At the same time, there is a decreasing availability or total absence of quality aggregates for construction in a number of regions in the U.S. and increasing cost and projected demand for asphalt. Sulfur's properties enable it to be used either as a structuring agent, taking the place of aggregate, or as an integral part of the binder or both.

Saylak notes that the use of sulfur in bituminous mixtures has been under study for some time in France and Cana­da. One way for it to be incorporated into an asphalt mix is through preparation of a sulfur-asphalt emulsion binder. Both

20 C&EN Nov. 22, 1976

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Nov. 22, 1976 C&EN 21

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Société Nationale des Pétroles d'Aqui­taine in France and Gulf Canada have processes involving proprietary tech­niques for such dispersal. Another way of incorporating sulfur is direct substitution for asphalt in simple blends of the mate­rials in a pug mill.

Both approaches now are being field tested, Saylak points out. A year ago, a series of test sections using emulsion binder with 30% by weight sulfur was placed along U.S. highway 69 north of Lufkin, Tex. And in the summer of 1975, a 500-foot test road using a directly sub­stituted sulfur-asphalt binder was placed in Ohio. Both are being evaluated.

Sulfur also can play a role, Saylak points out, in recycling old pavement. This use would take advantage of sulfur's ability to lower the viscosity of sulfur-asphalt dispersions below that of virgin asphalt and to increase the stiffness of the sulfur-asphalt-aggregate mixture when it cools to room temperature. A study of the use of sulfur in recycling is under way at the Texas Transportation Institute under sponsorship of the U.S. Bureau of Mines. Results to date, Saylak says, indicate that such use is favorable.

A variety of waste product systems has been studied over the past four years by Drexel University civil engineers Robert M. Koerner and Robert J. Schoenberger. Among those studied are incinerator ash, shells, coral, and crushed glass for use as aggregate; scrap steel and scrap polymer fibers as reinforcement; and lignite fly ash and blast furnace slag as cementing ma­terials. On the basis of conventional compression and bending tests, several systems show promise, the Drexel engi­neers say. Crushed glass, for example, was found to be an excellent aggregate re­placement, providing 80% of compressive strength of conventional materials. Scrap steel fibers look good as reinforcement, providing a 100% increase in flexural strength over unreinforced materials. And fly ash/slag cement was shown to be an excellent cementing material for building blocks, providing 85% of compressive strength of standard blocks.

Also looking at waste materials, Clem-son University civil engineer Parviz F. Rad has experimented with use of waste rubber from discarded tires as inert filler in portland cement concrete. Rad finds that rubberized concrete attains about 25% of the compressive strength and 35% of the tensile strength of conventional concrete, making it suitable for nonload bearing applications. Also, rubberized concrete has a relatively high resilience, toughness, and fracture surface energy, suggesting its use, Rad says, for energy-absorbing structures.

Along the same waste utilization lines, Rad looked at the technical feasibility of using tunnel boring machine muck (from hard rock tunneling operations) in port-land cement concrete. Results in this case indicate that the material can be used to make medium-strength concrete for ap­plications where very high strength isn't necessary—wall panels or dividers, for example.

Availability and low cost are prime considerations for construction materials in many areas, especially developing countries. One such material getting a great deal of attention is bamboo.

Consulting engineer K. R. Datye from Bombay, India, points out that the ulti­mate tensile strength of bamboo ranges from 1000 to 2000 kg per sq cm—about one fourth to one half that of mild steel. On the other hand, its unit weight is about one ninth that of steel. In India, he says, the cost of bamboo, without processing, ranges from about one fourth to one eighth that of steel. Thus, for equal strength, the cost of bamboo works out to about Vis to %o that of steel.

Such figures have prompted research on bamboo in a number of places. For example, Dr. Mahmoud Aly Reda Yous-sef, civil engineering professor at Cairo University, Egypt, has found in his re­search that completely seasoned or treated bamboo reinforcing rods—air-dried for at least 45 days—can increase the ultimate load-bearing capacity of a concrete beam four to five times that of an unreinforced beam.

One problem with bamboo when used for reinforcement is that it readily absorbs water from the wet concrete, expands, and then contracts, leaving a weak bond or even a space between it and the concrete matrix. Various researchers have used different treatments to combat the problem, with varying degrees of success. In his research, Youssef tried several water-repellent treatments, including a wood varnish, a blown bitumen paint, and a hard-grade bitumen. He finds that two brush coatings of the blown bitumen paint, followed by dusting with sand, works best.

A quite different approach to the problem of water absorbency has been taken by Dr. Hsai-Yang Fang, professor of civil engineering at Lehigh University and director of the conference. He has worked out a sulfur treatment as a tech­nique to increase bond strength and modulus and to reduce water absorption. In the technique, bamboo is sand blasted to remove the skin. It is then wrapped in wire such as chicken wire to prevent swelling. The pole is then soaked in liquid sulfur for an hour, and, before the sulfur completely dries, is coated with sand.

In addition to bamboo, date palm mid-ribs have been studied by Egypt's Youssef for similar purposes. He has found them to have much the same char­acteristics as bamboo.

In certain countries, rice husk presents the same benefits of low cost and avail­ability as do bamboo or date palm mid­ribs. Among a number of groups re­searching the construction material possibilities inherent in rice husks are Dr. Dinesh Mohan and Dr. S. M. Singh of the Central Building Research Institute, Roorkee, India.

Mohan and Singh point out that 10 million to 12 million tons of husk per year are obtained in India. A waste product, it is used mostly as fuel. The husks, they point out, are tough because of their sil-

22 C&EN Nov. 22, 1976

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Nov. 22, 1976 C&EN 23

PRODUCT PROSPECTUS ica-cellulose structural arrangement. On calcination, the husk gives an ash con­taining 90 to 95% silica, mostly amor­phous.

Research at the institute, Mohan and Singh say, has shown that particle boards of unburned rice husk bonded with port-land cement in a husk-cement ratio of 1:2 give good results. Panels of the material, they say, can be used for partitions, ceil­ings, and nonload bearing walls in low-cost houses.

Other investigations at the institute have shown that a product obtained after firing rice husk and clay in suitable pro­portions possessed good pozzolanic properties. When mixed with lime, the product produces a cementitious material. Likewise, rice husk burned with waste lime sludge and ground to fine powder was found suitable for masonry mortar and plaster. D

Ph.D. jobs growing fastest in industry Things were looking up for Ph.D. scien­tists and engineers from 1973 to 1975, according to recently released statistics from the National Science Foundation (C&EN, Nov. 8, page 9). With industry accounting for the largest increase of Ph.D. scientists and engineers during the two-year period, Ph.D. employment in­creased and unemployment dropped, despite a decline in Ph.D.'s receiving federal support in their work.

This is the picture that emerges from the second of a biennial series of surveys. The survey was conducted for NSF and the National Institutes of Health by the National Research Council of the Na­tional Academy of Sciences.

The total number of doctoral scientists and engineers grew 13% between 1973 and 1975, from 245,000 to 278,000. But the most notable change occurred in the em­ployment pattern, with industry ac­counting for an increase of 32%, from 50,000 to 66,000. In the two-year period, the proportion of Ph.D. scientists and engineers employed in industry increased from 22.1% of the total of those employed to 25.1%.

Women gained during the survey pe­riod. The number of men in the group increased 12%, but women posted a 23% increase. Thus women represented 9.4% of the total in 1975, compared to 8.7% in 1973.

Between 1973 and 1975, employment of Ph.D. scientists and engineers in­creased 16%. And the unemployment rate dropped from 1.2% in 1973 to just under 1% in 1975. The proportion of those em­ployed receiving federal funds in their work declined from 46% in 1973 to 43% in 1975.

In 1975, more than one third of em­ployed doctoral scientists and engineers were engaged in teaching. A bit less than one third were in R&D. And about one fifth were engaged in managerial activi­ties. D

24 C&EN Nov. 22, 1976

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