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NCAB Decisions 2011

12/2011 | 09/2011 | 07/2011 | 04/2011

Decisions of the National Coal Ash Board (NCAB) 12/2011

At the meeting of the NCAB held in December 2011, it was decided to continue to advance and promote research and development on the following subjects:

  • Construction – Determination of the benefits of the use of fly ash in concrete
  • Soil preservation – Stabilization of shifting sands using fly ash
  • Environment – Solubility of elements in a mix containing fly ash

These are the resolutions that were passed:

Effectiveness of fly ash used as a substitute for cement components and as a mean to reduce CO2 emission A study of the effectiveness of coal ash in cements of different types: Prof. Arnon Bentur, Prof. Amnon Katz, the National Building Research Institute at the Technion.
 
Brief overview
The production of clinker, which is the main raw material for cement, involves the emission of considerable amounts of CO2, known as a “greenhouse gas”. Taking advantage of the technological benefits of mineral alternatives such as fly ash can bring about a reduction in the emission of the greenhouse gas into the atmosphere.

The study is being conducted jointly with Nesher, a major cement producer, and the Association of Readymix and its objective is to prepare a technological infrastructure for the standardization of new high-quality cements and concretes containing a reduced amount of clinker. At an earlier stage of the study, an unsuccessful attempt was made to improve the replacement coefficient between coal ash and cement as dictated by the concrete standard, due to a change in the type of cement. At the current stage it is intended to ascertain that the benefit derived from the addition of the ash is maximized through technological coordination with the cement and concrete manufacturers.
 
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Fly ash to encourage the development of biogenic crusts in sandy soils to stabilize shifting sands An examination of the use of coal ash to stabilize soil surfaces to prevent erosion damage in sandy soil by encouraging the development of biogenic crusts. Dr. Eli Zaady, Gilat Research Center; and Dr. Yitzhak Katra of Ben-Gurion University in the Negev; Dr. Shlomo Sarig of the Katif Center; Dr. Naftali Goldshlager of the Erosion Station, Israeli Ministry of Agriculture.
 
Brief overview
The sandy soils in the northern Negev are naturally stabilized by biogenic crusts (which are formed by photosynthetic microorganisms) as long as they have not been exposed to anthropogenic (caused or produced by humans) disturbances. The preparation of land for agricultural use , executed by heavy equipment that flattens the surface, harms the natural stability of the soil surface, leading to the exposure of the newly developed agricultural areas to wind erosion damage.

The study will examine the hypothesis that the addition of fly ash to the upper soil layer stabilizes it and creates conditions that enable the redevelopment of biogenic crusts that stabilize the sandy soil.
 
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Test of pollutants in leachates of cement mixes containing coal ash used for infrastructures To determine the concentrations of trace elements in general, and specifically of heavy metals released from cement mixes containing fly ash in CLSM and grouts s intended for underground infrastructures. Dr. Nadya Teutsch, Geological Survey of Israel.
 
Brief overview
CLSM (Controlled Low Strength Materials) and grout are two types of cement slurry in which coal ash is used as a filler to improve the flow features.

In infrastructure applications, the CLSM and grout may come in contact with runoff water and even groundwater, and consequently it is important to measure the extent of the leaching of polluting elements as a result of the addition of coal ash to the slurry. The working assumption, based on tests carried out on samples in the past, is that the cement slurries containing ash, even at relatively high proportions, are safe for use underground and do not pose a danger to groundwater.
 
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Decisions of the National Coal Ash Board (NCAB) 9/2011

At the meeting of the NCAB held in September 2011, it was decided to continue to advance and promote research and development on the following subjects:

  • Construction – The effect of the origin of coal ash on concrete-quality indices
  • Environment – The effect of the environment surrounding the applied ash on the dissolution of trace elements in the ash

These are the resolutions that were passed:

The effect of the source of coal ash on concrete-quality indices The creation of a base of technological data which will help to assess the effect of ash from different sources on the performance of common concrete mixes. The purpose of the work is to characterize the contribution of the ash to the quality of the concrete as determined by a wide range of indices and to develop an optimization standard for these indices in order to enable the maximum exploitation of coal ash in concrete.
 
Brief overview
For the past five years, ever since the adoption of the updated version of the Israeli Standard 1209 dealing with – “Fly ash as an additive to concrete,” which is based on the European standard, the Coal Ash Board has been consistently monitoring the characterization of coal ash from different sources, according to the indices defined in this standard. The monitoring was originally intended to provide concrete manufacturers with the information they need to optimize the exploitation of coal ash in concrete.

As expected, concrete manufacturers are mainly interested in realizing the potential of replacing cement, the expensive component in concrete, with ash, which is permitted according to Israel Standard 118 (2008) – “Concrete: Demands, functioning and production”. However, coal ash affects important functional characteristics of concrete beyond the replacement of the cement. The main critical characteristics affected are:

  • The workability and cohesion of the fresh concrete
  • The development of concrete strength at early and later stages
  • The permeability of the hardened cement to liquids and gases.

These characteristics are dependent on the unique properties of the added coal ash, depending on its source. Such ash properties include:

  • The fineness of the particles and their size distribution
  • Residual uncombusted carbon
  • The chemical and mineralogical composition of the ash.

The required tests will be carried out in the laboratories of the Israel Standards Institute, according to a program prepared by Gideon Irus, advisor to the Coal Ash Board on the standardization of coal ash in concrete.

The effect of pH in the vicinity of applied fly ash on the leachability of trace elements from the ash In tests to be carried out in the Geological Institute under the direction of Dr. Nadya Teutsch, a pH characterization curve for elements released into a solution will be constructed for every type of ash (defined as originating from a given source).
 
Brief overview
The permission to use a coal ash in Israel for infrastructures, construction or agriculture is dependent on the characterization of the ash and its designation as “ash for a designated use.” This designation is dependent on the type of application and is determined to a large extent on the basis of the assessment of the extent of metal leaching from the ash-containing preparation under the environmental conditions created after a particular application of an ash. Studies conducted in Israel and research throughout the world show that the extent of dissolution of the various elements from the ash depends on the pH level in its vicinity. Every element has a different solubility dependence on the pH. In its different applications, the coal ash is exposed to environments with different typical pH levels; consequently, the assessment of the effect of the ash on its environment depends on understanding the effect of the environment (and in particular the pH level) on the ash.

Initial tests were carried out a few years ago on ash from various sources in the Geological Institute and at the Dutch ECN Institute, which served as a confirmatory scientific control.

The concentrations of the various elements obtained in the extraction solutions during the compliance tests which are carried out every year on ashes from all sources for regulatory purposes, will be examined as a function of the pH values measured in these solutions. This procedure will enable the construction of a pH vs. dissolution curve for every source of ash and will help to determine the environmental conditions suitable for its uses.

Decisions of the National Coal Ash Board (NCAB) 7/2011

At the meeting of the NCAB held in July 2011, it was decided to continue to advance and promote research and development on the following subjects:

  • Environment – The effect of the origin of ash on its contribution to reducing the exhalation of radon from concrete

These are the resolutions that were passed:

The effect of the orign of ash on its contribution to reducing the exhalation of radon from concrete Broadening of the database of characteristics of coal ash from various sources in order to add to existing documentation on the correlation between those characteristics and the effect of coal ash on the exhalation of radon from concrete in common mixes.
 
Brief overview
Radon exhalation depends on a number of factors, including the concentration of radium and thorium in the materials used in the preparation of the construction product and the product’s structure. Of course, most of the radon created in the ash is not emitted from it, and instead is extinguished inside the vitreous-amorphous structure of its particles. Furthermore, the addition of ash brings about the condensing of the concrete and thus inhibits the exhalation of radon even if its source is in other components of the cement. Ashes from different sources exhibit different particle size distributions and their pozzolanic efficiency (which contributes to the strengthening of the concrete) vary. Therefore, they may have a different effect on the exhalation of radon form construction products over time.

The tests, which will be carried out in the National Center for Radiation Safety at the Soreq Nuclear Research Center (NRC), are a continuation of the study on the effect of coal ash on radon exhalation from the walls of buildings over time, carried out in cooperation by researchers from the Technion and the Soreq center.

Decisions of the National Coal Ash Board (NCAB) 4/2011

At the meeting of the NCAB held in April 2011, it was decided to continue to advance and promote research and development on the following subjects:

  • Environment – To perform a trial run of the Dutch model to assess the effect of coal ash on the exhalation of radon from concrete
  • Agriculture – Bottom ash as a growth medium at a model pepper farm

These are the resolutions that were passed:

Assessing the effect of coal ash in concrete on exposure to radon A trial run of the Dutch model to assess the exposure to radon, as well as the general exposure to external (gamma) and internal (radon) radiation will be performed. The model will be considered as a professional comparative tool and an exposure assessment model that may serve as the basis for formulating the radiation standard for construction products in Israel.
 
Brief overview
In the framework of a study on the effect of coal ash on the exhalation of radon from concrete, conducted by a broad team of researchers from the National Building Research Institute at the Technion and the National Center for Radiation Safety (NCRS) at the Soreq Nuclear Research Center, identical concrete samples with and without coal ash were tested in the laboratories of the Technion, the Soreq NCRS and the NRG Institute in Holland.

Although the different laboratory tests found the concentrations of radioactive elements to be quite similar, they reported considerable differences in the radon exhalation findings: In the NRG laboratory, a reduction of 50% was obtained for the radon exhalation as a result of the addition of coal ash to the concrete, whereas in the laboratories in Israel, the reduction obtained was in the range of only 10%-20%.

The findings of the Dutch model make it possible to critically assess the results of the study and the recommendations that should emerge from it, based on international, expert judgment.

Bottom ash as a growth medium in a model pepper farm A three-year long experiment was conducted by the Central and Northern Arava Research and Development Unit in a model pepper farm in Paran to compare the behavior of coal ash in the capillary barrier-root zone with that of other growth media.
 
Brief overview
In view of the challenges involved in growing plants in the soils found in the Arava and the limited availability of both sand used to cover the soil (the accepted method in the past) and water of the required quality, the Arava R&D developed in recent years the “capillary barrier root zone” method as an effective growth method that is also economical in water use. A solid medium is placed in trenches dug into the soil on a basis of gravel and serves as a buffer to control percolation. The solid medium may include various components, such as inert aggregates with the appropriate particle size distribution, including coal ash or tuff.

Central and Northern Arava R&D initiated the establishment of a model farm (a commercial farm that allocates certain plots for controlled observations by experts) to compare various alternative media for the capillary barrier-root zone and was asked to test coarsely- sifted bottom ash (Matza’it) as the aggregate of choice.