Cement stabilised rammed earth. Part B: compressive strength and stress-strain characteristics

Strength and behaviour of cement stabilised rammed earth (CSRE) is a scantily explored area. The present study is focused on the strength and elastic properties of CSRE. Characteristics of CSRE are influenced by soil composition, density of rammed earth, cement and moisture content. The study is focused on examining (a) role of clay content of the soil on strength of CSRE and arriving at optimum clay fraction of the soil mix, (b) influence of moisture content, cement content and density on strength and (c) stress-strain relationships and elastic properties for CSRE. Major conclusions are (a) there is considerable difference between dry and wet compressive strength of CSRE and the wet to dry strength ratio depends upon the clay fraction of soil mix and cement content, (b) optimum clay fraction yielding maximum compressive strength for CSRE is about 16%, (c) strength of CSRE is highly sensitive to density and for a 20% increase in density the strength increases by 300-500% and (d) in dry state the ultimate strain at failure for CSRE is as high as 1.5%, which is unusual for brittle materials.

Proportioning of fly-ash cement concrete mixes

The accumulation of fly ash throughout the world is several million tons per day. The main problem with the usage of fly ash is the slow rate of strength gain, primarily due to slow pozzolanic reactions. Existing methods of proportioning fly ash concrete are lacking. These methods are involved and do not directly take into account the properties of the constituent materials. The Generalized Approach for Mix Proportioning developed at the Indian Institute of Science, Bangalore, is the basis for the development of the proposed method, which takes into account the characteristics of cement, fly ash, and aggregates. Based on the basic trial mix data obtained by using the American Concrete Institute (ACI 211.1-81) method, the proportions of fly-ash concrete mixes were arrived at using the Generalized Approach for Mix Proportioning. The method proposed was applied to and found applicable for fly-ash concretes using fly ashes from two different sources.

Structural Behavior of Story-High Cement-Stabilized Rammed-Earth Walls under Compression

A rammed-earth wall is a monolithic construction made by compacting processed soil in progressive layers in a rigid formwork. There is a growing interest in using this low-embodied-carbon building material in buildings. The paper investigates the strength and structural behavior of story-high cement-stabilized rammed-earth (CSRE) walls, reviews literature on the strength of CSRE, and discusses results of the compressive strength of CSRE prisms, wallettes, and story-high walls. The strength of the story-high wall was compared with the strength of wallettes and prisms. There is a nearly 30% reduction in strength as the height-to-thickness ratio increases from about 5 to 20. The ultimate compressive strength of CSRE walls predicted using the tangent modulus theory is in close agreement with the experimental values. The shear failures noticed in the story-high walls resemble the shear failures of short-height prism and wallette specimens. The paper ends with a discussion of structural design and characteristic compressive strength of CSRE walls. DOI: 10.1061/(ASCE)MT.1943-5533.0000155. (C) 2011 American Society of Civil Engineers.

Rice-Husk-Ash Cement - A Review

The use of silica from rice-husk for the production of various materials, including rice-husk ash-lime binder, has gained significance. In this context, the decomposition of husk, the properties of the silica ash, including its crystallization and the ash-lime reaction, are reviewed. The mechanism of ash-lime reaction is controlled mostly by the development of osmotic pressure. For lime-deficient ash-lime mixtures the reaction is complete in the initial few days and therefore no strength development is observed for such mortars in the later ages. The use of optimum ash/lime ratio is recommended for obtaining consistently good performance for the mortar. A method for the determination of this ratio is also discussed.

California bearing ratio behavior of cement-stabilized fly ash-soil mixes

Thermal power stations using pulverized coal as fuel generate large quantities of fly ash as a byproduct, which has created environmental and disposal problems. Using fly ash for gainful applications will solve these problems. Among the various possible uses for fly ash, the most massive and effective utilization is in geotechnical engineering applications like backfill material, construction of embankments, as a subbase material, etc. A proper understanding of fly ash-soil mixes is likely to provide viable solutions for its large-scale utilization. Earlier studies initiated in the laboratory have resulted in a good understanding of the California Bearing Ratio (CBR) behavior of fly ash-soil mixes. Subsequently, in order to increase the CBR value, cement has been tried as an additive to fly ash-soil mixes. This paper reports the results.

Role of clay content and moisture on characteristics of cement stabilised rammed earth

Rammed earth is an energy efficient and low carbon emission alternative for load bearing walls. This paper attempts to examine the influence of clay content and moisture content on the compressive strength of cement stabilised rammed earth (CSRE) through experimental investigations. Compressive strength of CSRE prisms was monitored both in dry and wet (saturated) conditions. Major conclusions of the study are:(a) Optimum clay content for maximum compressive strength is about 16%, (b) the strength of CSRE is sensitive to the moisture content at the time of testing, (c) Strength in saturated condition is less than half of the dry strength and (d) Water absorption (saturated water content) increases as the clay content of the soil mix increases and it is in the range of 12 to 16% for the CRSE prisms with 8% cement.

An experimental study on cracking evolution in concrete and cement mortar by the b-value analysis of acoustic emission technique

Notched three point bend (TPB) specimens made with plain concrete and cement mortar were tested under crack mouth opening displacement (CMOD) control at a rate of 0.0004 mm/s and simultaneously acoustic emissions (AE) released were recorded during the experiments. Amplitude distribution analysis of AE released during concrete was carried out to study the development of fracture process in concrete and mortar specimens. The slope of the log-linear frequency-amplitude distribution of AE is known as the AE based b-value. The AE based b-value was computed in terms of physical process of time varying applied load using cumulative frequency distribution (Gutenberg-Richter relationship) and discrete frequency distribution (Aki's method) of AE released during concrete fracture. AE characteristics of plain concrete and cement mortar were studied and discussed and it was observed that the AE based b-value analysis serves as a tool to identify the damage in concrete structural members. (C) 2012 Elsevier Ltd. All rights reserved.

Verification of Masonry Building Code to Flexural Behavior of Cement-Stabilized Soil Block

Most studies involving cement-stabilized soil blocks (CSSB) concern material properties, such as the characteristics of erosion and strength and how the composition of the block affects these properties. Moreover, research has been conducted on the performance of various mortars, investigating their material properties and the tensile bond strength between CSSB units and mortar. In contrast, very little is currently known about CSSB masonry structural behavior. Because structural design codes of traditional masonry buildings were well developed over the past century, many of the same principles may be applicable to CSSB masonry buildings. This paper details the topic of flexural behavior of CSSB masonry walls and whether the Masonry Standards Joint Committee (MSJC) code can be applied to this material for improved safety of such buildings. DOI: 10.1061/(ASCE)MT.1943-5533.0000566. (C) 2013 American Society of Civil Engineers.

SASW evaluation of asphaltic and cement concrete pavements using different heights of fall for a spherical mass

A number of spectral analysis of surface wave tests were performed on asphaltic and cement concrete pavements by dropping freely a 6.5kg spherical mass, having a radius of 5.82cm, from a height (h) of 0.51.5m. The maximum wavelength ((max)), up to which the shear wave velocity profile can be detected with the usage of surface wave measurements, increases continuously with an increase in h. As compared to the asphaltic pavement, the values of (max) and (min) become greater for the chosen cement concrete pavement, where (min) refers to the minimum wavelength. With h=0.5m, a good assessment of the top layers of both the present chosen asphaltic and the cement concrete pavements, including soil subgrade, can be made. For a given h, as compared to the selected asphaltic pavement, the first receiver in case of the chosen cement concrete pavement needs to be placed at a greater distance from the source. Inverse analysis has also been performed to characterise the shear wave velocity profile of different layers of the pavements.

Microcracking and fracture process in cement mortar and concrete: a comparative study using acoustic emission technique

This article reports the acoustic emission (AE) study of precursory micro-cracking activity and fracture behaviour of quasi-brittle materials such as concrete and cement mortar. In the present study, notched three-point bend specimens (TPB) were tested under crack mouth opening displacement (CMOD) control at a rate of 0.0004 mm/sec and the accompanying AE were recorded using a 8 channel AE monitoring system. The various AE statistical parameters including AE event rate , AE energy release rate , amplitude distribution for computing the AE based b-value, cumulative energy (I E) pound and ring down count (RDC) were used for the analysis. The results show that the micro-cracks initiated and grew at an early stage in mortar in the pre peak regime. While in the case of concrete, the micro-crack growth occurred during the peak load regime. However, both concrete and mortar showed three distinct stages of micro-cracking activity, namely initiation, stable growth and nucleation prior to the final failure. The AE statistical behavior of each individual stage is dependent on the number and size distribution of micro-cracks. The results obtained in the laboratory are useful to understand the various stages of micro-cracking activity during the fracture process in quasi-brittle materials such as concrete & mortar and extend them for field applications.

Low embodied energy cement stabilised rammed earth building-A case study

Rammed earth is a monolithic construction and the construction process involves compaction of processed soil in progressive layers in a rigid formwork. Durable and thinner load bearing walls can be built using stabilised rammed earth. Use of inorganic additives such as cement for rammed earth walls has been in practice since the last 5-6 decades and cement stabilised rammed earth (CSRE) buildings can be seen across the world. The paper deals with the construction aspects, structural design and embodied energy analysis of a three storey load bearing school building complex. The CSRE school complex consists of 15 classrooms, an open air theatre and a service block. The complex has a built-up area of 1691.3 m(2) and was constructed employing manual construction techniques. This case study shows low embodied energy of 1.15 GJ/m(2) for the CSRE building as against 3-4 GJ/m(2) for conventional burnt clay brick load bearing masonry buildings. (C) 2013 Elsevier B.V. All rights reserved.

Do stable isotopes in carbonate cement of Mio-Pleistocene Himalayan sediments record paleoecological and paleoclimatic changes?

Non-pedogenic carbonates, such as carbonate cement and nodules in the sandstones, are quite common in the terrestrial geological record. Unlike pedogenic carbonates, their stable isotope ratios lack investigations for paleo-climatic reconstructions. The present investigation therefore, explores the possibility of use of stable isotope studies of non-pedogenic carbonates from the Mb-Pleistocene Siwalik Group of sediments exposed in the Ramnagar sub-basin of the NW Himalaya. Petrographic studies reveal the dominance of micrite fabric in carbonate nodules both of pedogenic and non-pedogenic samples irrespective of specific stratigraphic unit However, calcite as cement in the sandstones shows the dominance of micrite fabric in the younger in age sediments. Seventy-two non-pedogenic carbonate samples from the carbonate nodules and cement in the Siwalik sandstones, ranging in age between similar to 1 Ma and 12.2 Ma, were analyzed for delta C-13 and delta O-18 values. The delta C-13 values vary from -24.77 parts per thousand to -1.1 parts per thousand and delta O-18 values vary from -15.34 parts per thousand to -7.81 parts per thousand. Pedogenic and non-pedogenic carbonates ranging in age between similar to 1 Ma and 6 Ma have largely similar delta C-13 values and the range of delta C-13 values indicate the dominance of C-4 type of vegetation. However, unlike pedogenic carbonates which showed the dominance of C-3 type of vegetation pre- 7 Ma on the basis of delta C-13 -depleted isotopic values (Singh et al., 2011), delta C-13 values are largely enriched in the corresponding aged non-pedogenic carbonates revealing no information on specific type of vegetation. Likewise, paleoprecipitational reconstructions from delta O-18 values in pedogenic carbonates showed a progressive increase in aridity from similar to 12 Ma to recent excluding short term increases in rainfall/monsoon intensity at around 10 Ma, 5 Ma, and 1.8 Ma (Singh et al., 2012). On the contrary, such reconstructions are not possible from the delta O-18 values of non-pedogenic carbonates and indeed the delta O-18 values of non-pedogenic carbonates are largely depleted to as much as 6 parts per thousand from the corresponding pedogenic carbonates. Such differences in delta C-13 and delta O-18 values of non-pedogenic carbonates from pedogenic carbonates are primarily due to the dependence of the former on groundwater conditions responsible for precipitating carbonate. Further, a comparison of isotopic values between non-pedogenic and pedogenic carbonates can be interpreted that post-6 Ma and pre-6 Ma non-pedogenic carbonates were largely formed by shallow and deep groundwater conditions respectively. The result of these investigative studies therefore, suggests that the stable delta C-13 and delta O-18 values of non-pedogenic carbonates, unlike the pedogenic carbonates and irrespective of nature of calcite fabric, showed their little importance in paleoclimatic and paleoecological reconstructions. (C) 2014 Elsevier B.V. All rights reserved.