Ethio - Construction

Part 2
# # # Core Cutter method.

Procedure of Core Cutter method.

👉Preparation:-

Find the volume of core cutter by measuring its internal dimensions. and find the weight of the core cutter (without dolly).

👉Sampling:-

Place the dolly over the cutter and drive the cutter into the soil with the help of rammer.
Take out the cutter containing soil.

👉Soil collection and Measuring:-

Remove the dolly and trim off the excess soil above the edges of the cutter. Take the weight of cutter filled with soil. take some representative sample for water content determination by the oven.

👉Calculations of Core Cutter method:-

The dry density of soil is computed as follows:

👉Weight of cutter =W1

👉Weight of soil + cutter = W2

👉Wt. of soil = W2-W1

👉Volume of cutter = V

👉Moisture content

/w/= (W.of soil –W.dry soil )* 100
W.dry soil

👉Bulk density
ϒ=W2-W1
V of cutter

👉Dry density ϒd= ϒ
1+w

"Field Density Test" (FDT), there are several different methods for determining the filed density of soils:-
1.Sand Replacement Method.
2.Core Cutter Method.
3.Rubber Balloon Method.
4.Heavy oil Method.

1.Sand Replacement Method.

👉 It is a test used to determine the in-situ or field density of soils.
👉Preparation:-
Prepare a hole in the ground at the location where you want to measure the density. Ensure that the hole is of a known volume.

👉Sampling:
Take a small representative soil sample from the hole. Measure its weight and moisture content, if needed.

👉Determination of Hole Volume:
Determine the volume of the hole by filling it with a known amount of sand and measuring the volume of sand used.

👉Sand Replacement:
Fill the hole with dry sand of known density. The sand is usually poured from a calibrated container.
*Care is taken to avoid air voids.

👉Excavation and Soil Collection:
Carefully excavate the soil from the hole and collect it in a container, ensuring there's no loss or spillage.

👉Weighing the Collected Soil:
Weight the collected soil from the hole.

👉Calculating Field Density:
The field density is then calculated using the weight of the soil and the volume of the hole.
Step #1
Field wet Density=(Wsample)
(Vhole)
Step #2
=W.Wet soil-W.dry soil *100
W.dry soil
=Moisture content.

Step #3
Field dry Density=FWet Density.
1+Mc/100.

👉The Field Density Test is significant in geotechnical engineering as it provides crucial information about the compactness and density of the soil in its natural state at the construction site.

👉This data is essential for making informed decisions regarding construction methods, compaction efforts, and the overall stability and performance of structures built on the site.

👉It helps engineers ensure that the soil is adequately compacted to support the intended structures.

Part #2

There are two methods of lunar concrete production;-

👉The first practice is lunar concrete made by mixing of Hydraulic cement as a binding material with Regolith Aggregate.In this case the most challenging is to find water, it is difficult to obtain it in the free state, it is experimentally obtained by chemical process of extracting from lunar soils.

👉The second practicing approach for preparation of lunar concrete is made from mixing of Lunar Aggregate with a binding agent like molten sulfur or epoxy (it is called waterless concrete)

👉Lunar concrete is produced in the precast element under control conditions of humidity and temperature should never be exposed to the vacuum until the hardening process is completed. Because it would reduce its properties to a considerable extent.

Lunar Concrete/የጨረቃ አርማታ/

Part #1

👉Lunar concrete is a type of concrete that is designed to be used in space exploration, it is made from a mixture of Lunar regolith, a type of soil found on the moon and Hydraulic cement or a binding agent such as melted sulfur powder, magnesium oxide or sodium silicate.

👉Idea first proposed by Larry A. Beyer of the University of Pittsburgh in 1985.

👉It is formed by using aggregate called lunar regolith this material is used as both coarse aggregate and fine aggregate.

👉Cement its produce on lunar surface by heating lunar soil or regolith to a temperature of 2000˚C under the solar panels.

👉Water there is no water currently in lunar surface, but by Hydrogen reduction mechanisms of ilmenite (FeTiO3) by using high temperature it’s possible to produce water.

Telegram: Contact @Eth1con

# # # Types of concrete cracks

1. 𝐏𝐥𝐚𝐬𝐭𝐢𝐜 𝐬𝐡𝐫𝐢𝐧𝐤𝐚𝐠𝐞 𝐜𝐫𝐚𝐜𝐤𝐬: These cracks are often shallow, irregular. They occur when the concrete is still in its plastic state and is drying too quickly.

2. 𝐃𝐫𝐲𝐢𝐧𝐠 𝐬𝐡𝐫𝐢𝐧𝐤𝐚𝐠𝐞 𝐜𝐫𝐚𝐜𝐤𝐬: These are hairline cracks that run parallel to each other and can occur anywhere in the concrete as it dries and shrinks.

3. 𝐓𝐡𝐞𝐫𝐦𝐚𝐥 𝐜𝐫𝐚𝐜𝐤𝐬: This type of cracks is caused by temperature changes in the concrete. Extreme heat or cold can cause the concrete to expand or contract, resulting in cracks.

4. 𝐒𝐞𝐭𝐭𝐥𝐞𝐦𝐞𝐧𝐭 𝐜𝐫𝐚𝐜𝐤s: These occur when the soil beneath the concrete settles or shifts, causing the concrete to crack and become uneven.

5. 𝐒𝐭𝐫𝐮𝐜𝐭𝐮𝐫𝐚𝐥 c𝐫𝐚𝐜𝐤𝐬: These are cracks that occur due to overloading or inadequate design or poor materials or poor construction, in this case the applied loads exceed the capacity of the concrete to resist. Structural cracks typically exceed 0.3 mm, and may continue to widen over time. Structural cracks may include: Shear cracks, Flexural cracks, Shear/flexural cracks, Torsion cracks.

6. 𝐂𝐨𝐫𝐫𝐨𝐬𝐢𝐨𝐧 𝐜𝐫𝐚𝐜𝐤𝐬: These are cracks caused by expansion of the reinforcement steel inside the concrete due to corrosion.

7. 𝐂𝐫𝐚𝐜𝐤𝐬 𝐝𝐮𝐞 𝐭𝐨 𝐀𝐥𝐤𝐚𝐥𝐢-𝐚𝐠𝐠𝐫𝐞𝐠𝐚𝐭𝐞 𝐫𝐞𝐚𝐜𝐭𝐢𝐨𝐧 (𝐀𝐀𝐑): This is a chemical reaction that occurs between the alkaline cement paste and certain types of aggregates in the concrete, resulting in a gel-like substance that can cause expansion and cracking over time. AAR can include alkali-silica reaction (ASR) and alkali-carbonate reaction (ACR).

Telegram: Contact @Eth1con

# # Methods of Evaluation and Selecting Consultants for Construction Projects.

👉Quality and cost based selection (QCBS):-uses a competitive process among short-listed firms that takes into account both the technical quality and the cost of the services proposed in the selection of the Consultant.

👉Quality Based Selection (QBS):-Is a selection process to determine the most appropriately qualified Consultant, based on technical competitiveness, integrity, professionalism etc. leading to a negotiated award of Consultancy services on a fair and reasonable basis.

👉Selection Under fixed Budgets (FBS):- This method is appropriate only when the assignment is simple and can be precisely defined and when the budget is fixed.

👉Selection of Consultants Qualifications (CQS):- This method may be used for small assignments of which the cost and time required for preparing and evaluating competitive proposals is not justified.

👉Selection Based on Least Cost:- This method is appropriate for procurement of a consultancy service which is standard, simple and doesn’t call for special qualification of a consultant.

# # Cement comparisons

# # OPC vs PPC

👉OPC has a relatively slow setting time and attains strength in a shorter time, while PPC takes longer.

👉OPC possesses excellent strength while the strength of PPC is good than OPC in long terms.

👉OPC best used for structures with the ability to bear heavy loads.

👉PPC best used for masonry, plastering and mass concrete works.
👉PPC has less Cost than of OPC.

👉PPC has grate resistance to aggressive weather while OPC is not favorable in aggressive weather.