← Project Management & Estimation · TNPSC AE Civil

Chapter 3 of 10

Cost control; quality control & inspection

In the TNPSC AE Civil syllabus under Project Management & Estimation · 2 parts

Cost Control & Earned Value Management · Quality Control & Quality Assurance

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📑 Contents (17 sections)

Part 1 of 2

Cost Control & Earned Value Management

Last reviewed 16 Sept 2026 · 5 min read

Cost control

Cost control ensures that the project is completed within the approved budget by comparing actual costs with planned costs and taking corrective action.

Steps

Prepare a budget (cost baseline) from the estimate, broken down by WBS/cost codes and time.
Record actual costs (labour, materials, equipment, subcontracts, overheads) against cost codes.
Measure work done (progress).
Compare planned, earned and actual costs; compute variances.
Forecast final cost; analyse causes and take corrective actions.
Report to management; update the plan.

Common causes of cost overrun

Inaccurate estimates and incomplete design; scope changes (variations).
Delays — approvals, land acquisition, utility shifting, slow payments, disputes.
Price escalation of materials and wages.
Low productivity, rework and poor quality; equipment breakdown.
Poor site management and wastage; unforeseen ground conditions.

Earned value management (EVM)

EVM integrates scope, schedule and cost to measure performance objectively.

Basic quantities

Term	Also called	Meaning
Planned value (PV)	BCWS — budgeted cost of work scheduled	Budgeted cost of work planned to be completed by the status date
Earned value (EV)	BCWP — budgeted cost of work performed	Budgeted cost of work actually completed by the status date
Actual cost (AC)	ACWP — actual cost of work performed	Actual cost incurred for the work completed
Budget at completion (BAC)	—	Total budget of the project

FormulaVariances and indices

Cost variance $C V = E V - A C$ (negative → over budget) Schedule variance $S V = E V - P V$ (negative → behind schedule)

Cost performance index $C P I = \frac{E V}{A C}$ ( $< 1$ → over budget) Schedule performance index $S P I = \frac{E V}{P V}$ ( $< 1$ → behind schedule)

FormulaForecasts

Estimate at completion (typical — current cost performance continues):

E A C = \frac{B A C}{C P I}

Atypical (remaining work at budget rate): $E A C = A C + (B A C - E V)$ Considering both CPI and SPI: $E A C = A C + \frac{B A C - E V}{C P I \times S P I}$

Estimate to complete $E T C = E A C - A C$ Variance at completion $V A C = B A C - E A C$

To-complete performance index (to finish within BAC):

T C P I = \frac{B A C - E V}{B A C - A C}

(Using EAC in the denominator instead: $T C P I = \frac{B A C - E V}{E A C - A C}$ .)

Rough time forecast: estimated duration ≈ planned duration / SPI

Interpretation

CPI	SPI	Status
> 1	> 1	Under budget, ahead of schedule
> 1	< 1	Under budget, behind schedule
< 1	> 1	Over budget, ahead of schedule
< 1	< 1	Over budget, behind schedule

TCPI > 1 — the remaining work must be done more efficiently than planned to meet the budget.
On an S-curve plot, the PV curve is the baseline; if the EV curve is below PV → behind schedule; if AC is above EV → over budget.

Part 2 of 2

Quality Control & Quality Assurance

Last reviewed 16 Sept 2026 · 7 min read

Quality

Quality is conformance to requirements (Crosby) or fitness for use (Juran) — meeting the specified and implied needs of the owner and users.

In construction, quality includes conformance to drawings and specifications, durability, safety, functionality, aesthetics and maintainability.

QC, QA and quality management

Term	Meaning
Quality control (QC)	Operational techniques — inspection, testing, measurement — to verify that products meet requirements; product-oriented, detects defects
Quality assurance (QA)	Planned and systematic activities (procedures, audits, documentation) to provide confidence that quality requirements will be met; process-oriented, prevents defects
Quality management	Overall management function — quality policy, planning, QC, QA and improvement
Total quality management (TQM)	Organisation-wide philosophy of continuous improvement with customer focus and involvement of all employees

Quality gurus

Contributor	Key ideas
W. Edwards Deming	PDCA (Plan–Do–Check–Act) cycle (Deming/Shewhart cycle); 14 points for management; reduce variation
Joseph M. Juran	Quality trilogy — quality planning, quality control, quality improvement; "fitness for use"; Pareto principle applied to quality (vital few, trivial many)
Philip B. Crosby	Zero defects; "quality is free"; conformance to requirements; cost of quality
Kaoru Ishikawa	Cause-and-effect (fishbone) diagram; quality circles
Walter A. Shewhart	Control charts; statistical process control
Armand Feigenbaum	Total quality control; cost of quality
Genichi Taguchi	Loss function; robust design

ISO 9001

ISO 9001 specifies requirements for a quality management system (QMS); the current edition is ISO 9001:2015 (as of the update date of these notes).
Principles include customer focus, leadership, engagement of people, process approach, improvement, evidence-based decision making, relationship management; the 2015 edition emphasises risk-based thinking.
Certification is by accredited third-party bodies.

Quality planning in construction projects

Quality assurance plan (QAP) — scope, organisation and responsibilities, procedures, standards, testing frequencies, documentation.
Inspection and test plan (ITP) — for each activity: what to inspect/test, method, frequency, acceptance criteria, hold points (work cannot proceed until inspected) and witness points.
Method statements, checklists, material approvals (samples, mill certificates), field laboratory, third-party quality audits, non-conformance reports (NCR) and corrective/preventive actions.

Seven basic quality control tools

Check sheet — structured data collection.
Histogram — frequency distribution of data.
Pareto chart — defects ranked by frequency — about 80% of problems from 20% of causes.
Cause-and-effect (Ishikawa/fishbone) diagram — causes grouped (e.g. man, machine, material, method, measurement, environment).
Scatter diagram — relationship between two variables.
Control chart — process variation over time.
Stratification (or flow chart in some lists) — separating data by source.

Statistical quality control

Control charts

A control chart plots a quality characteristic over time with a centre line (CL), upper control limit (UCL) and lower control limit (LCL), commonly at ±3σ of the plotted statistic.

Chart	For	Plots
x̄ chart	Variables	Sample means — process average
R chart / s chart	Variables	Sample ranges / standard deviations — dispersion
p chart	Attributes	Fraction defective
np chart	Attributes	Number defective (constant sample size)
c chart	Attributes	Number of defects per unit

FormulaControl limits

x̄ chart: $U C L = \overset{ˉ}{\overset{x}{ˉ}} + A_{2} \overset{ˉ}{R}$ , $L C L = \overset{ˉ}{\overset{x}{ˉ}} - A_{2} \overset{ˉ}{R}$ R chart: $U C L = D_{4} \overset{ˉ}{R}$ , $L C L = D_{3} \overset{ˉ}{R}$ p chart: $\overset{p}{ˉ} \pm 3 \frac{p ˉ ( 1 - p ˉ )}{n}$ c chart: $\overset{c}{ˉ} \pm 3 \overset{c}{ˉ}$ (Negative LCL is taken as zero.)

Points outside limits or non-random patterns (runs, trends) indicate assignable (special) causes; variation within limits is due to chance (common) causes.
Process capability $C_{p} = \frac{U S L - L S L}{6 σ}$ — $C_{p} \geq 1.33$ is commonly regarded as capable.

Acceptance sampling

Deciding to accept or reject a lot based on a sample.
Producer's risk (α) — rejecting a good lot; consumer's risk (β) — accepting a bad lot.
Operating characteristic (OC) curve — probability of acceptance vs lot quality; AQL (acceptable quality level) and LTPD (lot tolerance percent defective).

Cost of quality

Category	Examples
Prevention costs	Training, quality planning, process design
Appraisal costs	Inspection, testing, audits
Internal failure costs	Rework, scrap, repairs before handover
External failure costs	Defects after handover — repairs, claims, reputation loss

Investing in prevention reduces failure costs — the total cost of quality falls.

Six Sigma

Data-driven approach to reduce variation; a Six Sigma process has about 3.4 defects per million opportunities (DPMO) (allowing a 1.5σ shift).
Methodology DMAIC — Define, Measure, Analyse, Improve, Control; roles such as Champions, Black Belts and Green Belts.

Quality control of concrete

FormulaTarget mean strength (IS 10262)

f_{c k}^{'} = f_{c k} + 1.65 s

$s$ = standard deviation (assumed values are given in IS 10262 when site data are not available); 1.65 corresponds to not more than 5% of results falling below $f_{c k}$ .

Sampling frequency (IS 456)

Quantity of concrete in the work (m³)	Number of samples
1–5	1
6–15	2
16–30	3
31–50	4
51 and above	4 + 1 for each additional 50 m³ or part

Each sample consists of three cubes; the sample strength is the average of the three (individual variation limits apply).
Acceptance is judged using the mean of groups of consecutive non-overlapping results and individual results relative to $f_{c k}$ , as specified in IS 456 (as amended).

Other site QC for concrete

Tests on materials — cement (setting time, soundness, strength), aggregates (grading, silt, flakiness), water.
Slump test for workability; temperature; air content where required.
Non-destructive tests on hardened concrete — rebound hammer (surface hardness), ultrasonic pulse velocity (homogeneity, cracks), cover meter, half-cell potential (corrosion risk), core tests (actual strength).

Worked examples

Worked ExampleExample 1 — target mean strength

Find the target mean strength for M25 concrete with a standard deviation of 4 N/mm².

Solution. $f_{c k}^{'} = 25 + 1.65 \times 4 =$ 31.6 N/mm²

Worked ExampleExample 2 — number of samples

How many cube samples are required for 140 m³ of concrete in a slab, and how many cubes?

Solution. Up to 50 m³: 4 samples; the remaining 90 m³ is one full 50 m³ plus a part → 2 more samples. Total = 6 samples = 18 cubes

Worked ExampleExample 3 — p chart limits

In 20 samples of 50 bricks each, the average fraction defective is 0.04. Find the control limits.

Solution. $σ_{p} = \frac{0.04 \times 0.96}{50} = 0.0277$ UCL $= 0.04 + 3 \times 0.0277 =$ 0.123; LCL $= 0.04 - 0.083 < 0$ → 0

Worked ExampleExample 4 — Pareto analysis

Defects in plaster: hollow sound 45, cracks 30, uneven surface 15, stains 6, others 4. Which defects should be tackled first?

Solution. Total = 100. Hollow sound (45%) and cracks (30%) together account for 75% of defects → address these first.

Frequently tested points

QC = inspection/testing (product, detect); QA = systematic process (prevent, confidence); TQM = organisation-wide continuous improvement.
Deming — PDCA; Juran — trilogy, fitness for use; Crosby — zero defects, quality is free; Ishikawa — fishbone, quality circles; Shewhart — control charts.
ISO 9001 — QMS standard (2015 edition).
Seven QC tools: check sheet, histogram, Pareto, fishbone, scatter, control chart, stratification/flow chart.
Control charts: x̄ and R (variables); p, np, c (attributes); limits ±3σ.
Cost of quality: prevention, appraisal, internal failure, external failure.
Six Sigma: 3.4 DPMO; DMAIC.
Target mean strength $f_{c k} + 1.65 s$ ; IS 456 sampling: 1, 2, 3, 4 samples for up to 5, 15, 30, 50 m³, then +1 per 50 m³; 3 cubes per sample.
NDT: rebound hammer, UPV, cover meter, half-cell potential, cores.

Common MistakeCommon mistakes

Using QC and QA interchangeably.
Using p charts for number of defects per unit (use c charts).
Counting cubes instead of samples when applying IS 456 sampling frequency.

Revision SummaryChapter summary

Quality means conformance to requirements and fitness for use; QC inspects products while QA assures processes.
Deming, Juran, Crosby, Ishikawa and Shewhart shaped TQM, PDCA, zero defects, fishbone diagrams and control charts.
ISO 9001, quality assurance plans and inspection and test plans structure project quality management.
Seven QC tools, control charts, acceptance sampling, cost of quality and Six Sigma support improvement.
Concrete quality is controlled through target mean strength, sampling frequency, acceptance criteria and non-destructive testing.

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