Compressed earth blocks (CEB) compression tested under two earth standards

Abstract

Building with raw earth is a responsibility that translates into safe, low-impact and small carbon footprint constructions. However, beyond its current use, it is imperative to validate the different earth construction systems, starting with their components, under standards that ensure the safety of this type of constructions. In countries where construction with earth is allowed, it is verified by Standards and Technical Documents or Construction Regulations. Therefore, the objective of the research is to contrast a series of compressed earth blocks (CEB) subjected to compression tests with the Brazilian and Colombian standards, and the Mexican standards with clay soils in the region, identifying the deviations between the results and their possible causes. In the results, it was observed that the compression test procedure varies for each Standard, the Brazilian and Colombian Standards being similar, and these in turn adhere more to the construction system, while with the Mexican Standard the results are higher than the previous one since the norm requires to test the complete block.

Keywords:

• construction with earth
• technical standards
• compressive strength

1. Introduction

It is a priority that the new generations of architects and construction engineers use alternative materials to build that have a low environmental impact, which is why earthen architecture is offered as a possible solution, since the construction industry is one of the most polluting (Vera, 2019).

The data is that for every ton of cement with silicates that is produced, a ton of CO2 is emitted into the environment. Therefore, the great challenge for future generations is, in addition to the use of alternative materials, the validation of the safety of these construction techniques with Technical Standards and scientific methods, such as laboratory tests for these constructions.

Compressed Earth Blocks or CEBs are one of the methods for using earth as a building material. This construction system is based on the elaboration of masonry blocks, which are made up of earth, water and some type of stabilizer (cement, straw, vegetable fibers and lime), in addition to using certain percentages of sand. This mixture is previously placed in a mold and then compressed by a press, to reduce the air between particles and thus increasing the density of the block and improving its mechanical properties. After this, the block is removed from the mold and left to dry in the open air. (Sitton et al., 2018).

CEB masonry is an economic construction technique that has better resistance and durability properties than those built with adobe and has great potential for the industrialization of its units (Herrera Villa, 2018). In addition, these blocks have several advantages that allow them to face current energy and climate problems, as they are elements made with low energy consumption materials (Bradley et al., 2018), compared to fire bricks and concrete blocks, reducing the total energy required for construction and transportation, due to the fact that earth is an abundant and reusable natural resource (Ben Mansour et al., 2017; Hegyi et al., 2016).

Construction with earth has three large families of construction systems: mixed structures, monolithic walls, and masonry. These systems basically refer to walls and can be load-bearing or simply dividing (Gómez-Patrocinio et al., 2021).

From the previous classification, within the system of mixed structures, several types arise, such as: cob frame, smeared earth, filler and lightened straw. Within the monolithic walls are rammed earth, poured earth, direct and excavated formwork. In masonry there are adobes with mold and adobes molded by hand, extruded earth, and compressed earth blocks, among others (Houben & Guillaud, 1994).

The practice of stabilization in earthen construction in general is important as it helps to improve the physical characteristics of the soil, either by increasing compressive strength, tensile strength, or reducing cracks caused by clay shrinkage, whether they are masonry elements, mixed structures, or monolithic walls. Stabilizers can be of plant origin such as fibers and saps; of animal origin such as animal hair, horse manure; or of mineral origin such as cement and lime (Pelé-Peltier et al., 2022). With lime, an ionic exchange occurs between clay and lime, the latter functioning as a stabilizer if there is sufficient moisture (Cabrera et al., 2020).

The calcium ions in the lime are exchanged with the metal ions in the clay; when the soil is also rich in pozzolana, it is recommended to use lime as a stabilizer. Since the clay will act as a binder, in low content soils the mineral stabilizer should be increased. In some cases, Portland cement is used, however, stabilizing it with percentages higher than 6% is no longer considered sustainable.

Some of these construction procedures have standards and others do not, highlighting most of the standards for masonry systems and monolithic walls. The Latin American countries that have Territorial Regulations are described in Table 1.

Table 1. Main regulations in Latin America. Source: The authors

COUNTRY	STANDARDS	FEATURES
Argentina	Laws, Local and Municipal Ordinances; International Technical Standards	Raw earth is used in a large percentage.
Brazil	Associação Brasileira de Normas Técnicas, ABNT (2012) on walls and masonry	The process to test the CEB in compression is to split the block in half and join the two halves with mortar and thus subject it to the load.
Chile	Technical Standard NCH 3332, technical documents, and recommendations	Regarding the intervention of heritage buildings
Colombia	Technical Standard NTC 5324 (based on the French standard) and technical documents.	As in the procedure for preparing the specimens, it mentions splitting the blocks in half and joining them with mortar to later test them.
El Salvador	Regulations and Technical Criteria	In relation to adobe constructions for single-story dwellings.
Guatemala	National Construction Regulations and Regulations for Heritage Buildings and Intervention	The purpose of this Regulation is to establish the guidelines to follow in terms of new construction and interventions in old buildings and other types of constructions or buildings in public or private property, which are carried out in La Antigua Guatemala, surrounding areas and zone of influence. .
Mexico	Standard CEB stabilized with lime, Mexican Standard ONNCCE 508–2015 for CEB, Standards for heritage and conservation	The heritage and conservation regulations have in their procedure to test the CEB to compression.
Peru	Technical Standard for Design and Construction with Reinforced Earth E080, Technical Standards for adobe and Technical Documents for reinforced adobe	The standard refers to the mechanical characteristics of the materials for the construction, to the earthquake resistant, and the structural elements of reinforced earth buildings, as well as the behavior of adobe and rammed earth walls.

Derived from the information shown in Table 1, this study focuses on the very similar Colombian Standard NTC 5324 (2018) and Brazilian Standard ABNT, and the Mexican Standard NMX-C-508-ONNCCE-2015 (2015). From this comparison it can be concluded that there are many similarities between the different Latin American regulations (and from other parts of the world). For example, the Colombian standard is a translation of the French; and in both Colombian and Brazilian standards, the block is split in two for testing. While Mexican regulations work with the complete block.

2. Methodology

The objective of this work is to contrast the results obtained from compression tests with two compressed earth standards, (Brazilian which is like Colombian and Mexican standards) made with clay soil in the region, identifying the deviations between results and their possible causes.

In the materials laboratory of the Faculty of Architecture, Design and Urbanism of the Autonomous University of Tamaulipas, Mexico, 30 samples were prepared. For this work, CEBs were made in the form of a rectangular prism of 0.095 × 0.144 x 0.295 m in a manual Cinva-Ram type press (Figure 1).

Figure 1. Cinva-Ram press.

Sample material: Clay soil from the area, river sand and were stabilized with 6% Portland cement. Stabilization is important because more than 10% of cement is considered no longer sustainable.

For the elaboration of 30 test tubes, 18 kg of earth were required:

• Clay soil: 18 kg

• Medrano: 2 kg, sand-loam type soil, owes its name to the local material bank

• Cement: 1,200 kg

• Water: 1 liter

3. Composition of the groups that were tested

To carry out the tests, four main groups were developed with characteristics that consider the possibilities in testing by different international standards. The four groups were called A, B, C and D. The description of each of them is detailed below.

Group A: Entire blocks that were tested according to the procedure of the Mexican ONNCCE Standard 508–2015

Group B: Half blocks

Group C: Half a block supported on another half block and without mortar

Group D: Half a block settled with cement-sand mortar on another half block, this would correspond to the NTC 5324 section 4.5.2 and the NTB Brazilian Technical Standard in its latest version NBR 8492–2012.

From each of the series or groups, 7 samples or test tubes were made, leaving 2 test tubes or CEB in reserve.

Groups B and C decided to test half blocks since in the quadruped rigging of the walls they are occupied by this same arrangement or formal arrangement, particularly at the ends and this is a situation that occurs in the construction of a wall. In these groups, mortar is also not used to verify its effect in group D.

In group D, it was determined to test the two half blocks settled with cement-sand mortar in a 1:3 ratio to observe the contribution of the mortar when contrasting it with the results of group C.

The blocks were tested 30 days after manufacture. For the compression test, a press was used: Controls, Serial No. 02116512 Capacity 1000 kN (Figure 2). To carry out the test, 2 plates were used, which served to distribute the load in the blocks, as seen in Table 2.

Figure 2. Controls press for compression tests.

Source: Yolanda Aranda, Ph.D.

Table 2. Compression results of the different groups elaborated. Source: The authors

Sample Number	Grup A Whole Block		Grup B Half Block Hz		Grup C Half Block—supported over half block		Grup D Half Block- settled w/mortar w/o half block
	Load	Effort	Load	Effort	Load	Effort	Load	Effort
1	18 672 kg.	45.99 kg/ cm^2	8 383 kg.	41. 2 kg/ cm^2	3 743 kg.	18.439 kg/ cm^2	4 204 kg.	21.4 kg/ cm^2
2	18 247 kg.	44.94 kg/ cm^2	6 587 kg.	31.7 kg/ cm^2	4 317 kg	21.114 kg/ cm^2	5 433 kg.	26.7 kg/ cm^2
3	20 156 kg.	49.53 kg/ cm^2	5 607 kg.	28.20 kg/ cm^2	4 082 kg	20.11 kg/ cm^2	5 417 kg.	27.04 kg/ cm^2
4	17 890 kg.	44.06 kg/ cm^2	6 813 kg.	32.34 kg/ cm^2	3 974 kg.	19.036 kg/ cm^2	4 707 kg.	23.02 kg/ cm^2
5	19 756 kg.	48.54 kg/ cm^2	10 440 kg.	50.35 kg/ cm^2	3 550 kg.	17.244 kg/ cm^2	5 735 kg.	28.24 kg/ cm^2
6	21 194 kg.	52.07 kg/ cm^2	7 550 kg.	36.67 kg/ cm^2	3 750 kg.	18.599 kg/ cm^2	5 195 kg.	25.23 kg/ cm^2
7	22 086 kg.	54.40 kg/ cm^2	9 418 kg.	45.42 kg/ cm^2	3 540 kg.	17.192 kg/ cm^2	5 391 kg	26.92 kg/ cm^2

4. Analysis of results

The samples of series A maintain an average value of the compression rupture stress of 48,504 kg/cm2. and with a standard deviation of 3.815. The values obtained from the efforts are maintained without significant variations between them.

Series B, in which the load is applied to half of a block, shows a significant reduction in the value of the average compressive stress of levels of 37.983 kg/cm2, showing an important reduction with respect to series A of the order of 21.692%, and a greater dispersion with a standard deviation of 8.035, motivated by the concentration of the charge when the contact surface is reduced.

Series C, in which two half blocks are stacked without a mortar joint, shows a decrease in compression stress of 18.819 kg/cm2, and a standard deviation of 1.432. The average value of compressive strength is 50.454% lower than that obtained in series B, which suggests that the irregular union of the faces of the samples has an important influence on the resistance of the blocks.

Series D, which consists of a half block set with mortar on another half block, shows a recovery in resistance with respect to series C, when correcting the irregularity of the joint by means of the presence of mortar. The average resistance is located at a value of 25,507 kg/cm2, with a standard deviation of 2.462 kg/cm2. The average compressive strength value of this series is 35.538% higher than that of series C.

Given that the joint between blocks without mortar is unstable if a padlock is not placed on the surface of the element, and that the walls would be built with stacked blocks and with a rig that limits the vertical lines of failure, it is recommended to use the information of the blocks joined with mortar as a loading system.

It is also suggested to carry out compression tests with low walls jointed with mortar, since this more directly represents the behavior of the walls of a house subjected to compression generated by floor loads.

5. Conclusions

Given the resistance obtained in each of the groups, it is feasible to propose a system based on walls jointed with mortar, to receive the loads of the floor system.

According to the results obtained from Group A that are attached to the procedure of the Mexican Standard of ONNCCE 508–2015 for compressed earth blocks, an average of 48,504 kg/cm2 was obtained, where type 3 indicates that the CEB must have a resistance to the minimum compression of 30 kg/cm2 so it is within the norm. The element that was tested in isolation is part of a more complex system that involves the joining and rigging method, which is why the other groups were tested. The resistance achieved by this group is superior to the others.

With respect to series B, as mentioned in the analysis of results, the compressive strength is significantly decreased by 21.692%, which must be considered when making the rigging and building the wall. In some construction systems based on CEB, instead of splitting the blocks in half, it is preferred to lock them in the corners by passing them alternately.

The D series, which is attached to the Colombian Technical Standard NTC 5324, section 4.5.2, increases its load capacity, due to the mortar that joins both halves, reaching an average value of 25,507 kg/cm2, which compared to the Group C increased by 35,538%. This series reflects in a more attached way to the construction how the material would be used.

Finally, responding to the initial questions, we must adhere to the regulations that govern the country where the earthen project will be built. If there are none, they can be validated by the afore mentioned land regulations, as long as they adhere to the masonry construction system.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

The authors received no direct funding for this research.

Notes on contributors

Yolanda Aranda-Jiménez

Yolanda G Aranda-Jimenez has a Ph.D. in Architecture with emphasis in housing by the Universidad Autonoma de Tamaulipas; is a professor and UNESCO Cathedra Representative For Earthen Architecture since 2012 for the Faculty of Architecture, Design and Urbanism of the Universidad Autonoma de Tamaulipas, Mexico; a member of the PROTERRA Network since 2005, a member of the SNI 1 (National Investigators System Level 1, in Mexico) since 2016, and member of the Mesoamerica Network since 2019; published several indexed articles (Aranda-Jiménez); published the book “Tierra Vertida” (Principal author: Aranda-Jiménez, 2020).With a broad interest in earthen architecture and its research, she has participated in various international conferences and taught workshops on building with Earth, as well as continuous research in the subject, with the purpose of promoting this type of construction as a more sustainable alternative through safe and standard regulated practices.